Refrigerating Apparatus and Air Conditioner

ABSTRACT

An air conditioner has a refrigerant circuit and a first oil returning circuit. The refrigerant circuit has a plurality of utilization refrigerant circuits each having a utilization heat exchanger and a utilization expansion valve connected to a heat source refrigerant circuit that includes a compression mechanism, a heat source expansion valve and a heat source heat exchanger configured so that a refrigerant flows in from below and flows out from above when the heat source heat exchanger functions as an evaporator. The heat source refrigerant circuit uses a combination of a refrigerating machine oil and a refrigerant that does not separate into two layers in a temperature range of 30° C. or below. The first oil returning circuit is connected to a lower portion of the heat source heat exchanger and returns the refrigerating machine oil accumulated inside the heat source heat exchanger to the compression mechanism together with the refrigerant.

TECHNICAL FIELD

The present invention relates to a refrigerating apparatus and an airconditioner, and particularly relates to a refrigerating apparatus andan air conditioner provided with a refrigerant circuit that has anevaporator configured so that refrigerant flows in from below and flowsout from above.

BACKGROUND ART

Conventionally, there has been a refrigerating apparatus disposed with avapor compression-type refrigerant circuit including a heat exchangerconfigured such that refrigerant flows in from below and flows out fromabove as an evaporator of the refrigerant (e.g., see Patent Document 1).In order to prevent refrigerating machine oil from accumulating insidethe evaporator, the refrigerating apparatus is configured to extract,from the vicinity of the surface of the refrigerant, the refrigeratingmachine oil accumulating in a state where it floats on the surface ofthe refrigerant as a result of the refrigerating machine oil and therefrigerant separating into two layers because the specific gravity ofthe refrigerating machine oil is smaller than that of the refrigerant,and to return the refrigerating machine oil to the intake side of thecompressor.

Further, as an example of a refrigerating apparatus disposed with avapor compression-type refrigerant circuit, there is an air conditionerdisposed with a vapor compression-type refrigerant circuit including: aheat source refrigerant circuit including plural heat source heatexchangers; and plural utilization refrigerant circuits connected to theheat source refrigerant circuit (e.g., see Patent Document 2). In thisair conditioner, heat source expansion valves are disposed so that theflow rate of the refrigerant flowing into the heat source heatexchangers can be regulated. Additionally, in this air conditioner, whenthe heat source heat exchangers are caused to function as evaporatorsduring a heating operation or during a simultaneous cooling and heatingoperation, for example, control is conducted to reduce the evaporatingability by reducing the openings of the heat source expansion valves asthe overall air conditioning load of the plural utilization refrigerantcircuits becomes smaller. Moreover, when the overall air conditioningload of the plural utilization refrigerant circuits becomes extremelysmall, control is conducted to reduce the evaporating ability by closingsome of the plural heat source expansion valves to reduce the number ofheat source heat exchangers functioning as evaporators or to reduce theevaporating ability by causing some of the plural heat source heatexchangers to function as condensers to offset the evaporating abilityof the heat source heat exchangers functioning as evaporators.

Further, in the aforementioned air conditioner, when the heat sourceheat exchangers are caused to function as condensers during a coolingoperation or during the simultaneous cooling and heating operation,control is conducted to reduce the condensing ability by increasing theamount of liquid refrigerant accumulating inside the heat source heatexchangers and reducing the substantial heat transfer area by reducingthe openings of the heat source expansion valves connected to the heatsource heat exchangers as the overall air conditioning load of theplural utilization refrigerant circuits becomes smaller. However, whencontrol is conducted to reduce the openings of the heat source expansionvalves, there is the problem that there is a tendency for therefrigerant pressure downstream of the heat source expansion valves(specifically, between the heat source expansion valves and the pluralutilization refrigerant circuits) to drop and become unstable, andcontrol to reduce the condensing ability of the heat source refrigerantcircuit cannot be stably conducted. In order to counter this problem,control has been proposed to raise the refrigerant pressure downstreamof the heat source expansion valves by disposing a pressurizing circuitthat causes high-pressure gas refrigerant compressed by the compressorto merge with refrigerant whose pressure has been reduced in the heatsource expansion valves and is sent to the utilization refrigerantcircuits (e.g., see Patent Document 3).

Patent Document 1

-   -   Japanese Patent Application Publication No. S63-204074

Patent Document 2

-   -   Japanese Patent Application Publication No. H03-260561

Patent Document 3

-   -   Japanese Patent Application Publication No. H03-129259

DISCLOSURE OF THE INVENTION

In the aforementioned air conditioner, there are cases where a heatexchanger such as a plate heat exchanger configured such that therefrigerant flows in from below and flows out from above whenfunctioning as an evaporator of the refrigerant is used as the heatsource heat exchangers. In these cases, in order to prevent therefrigerating machine oil from accumulating inside the heat source heatexchangers, it is necessary to maintain the level of the refrigerantinside the heat source heat exchangers at a constant level or more.However, even if one tries to reduce the amount of refrigerant flowingthrough the heat source heat exchangers by reducing the openings of theheat source expansion valves when the heat source heating exchangers arecaused to function as evaporators with little evaporating ability, suchas when the air conditioning load in the plural utilization refrigerantcircuits becomes extremely small, the evaporating ability cannot besufficiently controlled just by regulating the openings of the heatsource expansion valves because the openings of the heat sourceexpansion valves cannot be reduced that much due to the restriction ofthe level of the refrigerant inside the heat source heat exchangers. Asa result, it becomes necessary to conduct control to reduce theevaporating ability by closing some of the plural heat source expansionvalves to reduce the number of heat source heat exchangers functioningas evaporators or to reduce the evaporating ability by causing some ofthe plural heat source heat exchangers to function as condensers tooffset the evaporating ability of the heat source heat exchangersfunctioning as evaporators.

For this reason, there are the problems that increases in the number ofparts and cost arise as a result of disposing plural heat source heatexchangers, the amount of the refrigerant compressed in the compressorincreases in correspondence to the amount of refrigerant condensed bythe heat source heat exchangers when some of the plural heat source heatexchangers are caused to function as condensers to reduce theevaporating ability, and the COP becomes poor in an operating conditionwhere the overall air conditioning load of the plural utilizationrefrigerant circuits is small.

Further, in the aforementioned air conditioner, when a pressurizingcircuit is disposed in the refrigerant circuit to cause thehigh-pressure gas refrigerant compressed by the compressor to merge withthe refrigerant whose pressure has been reduced in the heat sourceexpansion valve and which is sent to the utilization refrigerantcircuits when the heat source heat exchangers are caused to function ascondensers of the refrigerant, the refrigerant sent from the heat sourceexpansion valve to the utilization refrigerant circuits becomes agas-liquid two-phase flow. Moreover, the gas fraction of the refrigerantafter the high-pressure gas refrigerant has merged therewith from thepressurizing circuit becomes larger the more the openings of the heatsource expansion valves are reduced, and drift arises between the pluralutilization refrigerant circuits, resulting in the problem that theopenings of the heat source expansion valves cannot be sufficientlyreduced. As a result, similar to when the heat source heat exchangersare caused to function as evaporators of the refrigerant, when pluralheat source heat exchangers are disposed in the heat source refrigerantcircuit and the overall air conditioning load of the plural utilizationrefrigerant circuits becomes extremely small, it becomes necessary toconduct control to reduce the condensing ability by closing the pluralheat source expansion valves to reduce the number of heat source heatexchangers functioning as evaporators or to reduce the condensingability by causing some of the plural heat source heat exchangers tofunction as evaporators to offset the condensing ability of the heatsource heat exchangers functioning as condensers.

For this reason, there are the problems that increases in the number ofparts and cost arise as a result of disposing plural heat source heatexchangers, the amount of the refrigerant compressed in the compressorincreases in correspondence to the amount of refrigerant evaporated bythe heat source heat exchangers when some of the plural heat source heatexchangers are caused to function as evaporators to reduce thecondensing ability, and the COP becomes poor in an operating conditionwhere the overall air conditioning load of the plural utilizationrefrigerant circuits is small.

It is an object of the present invention to provide a refrigeratingapparatus and an air conditioner comprising a refrigerant circuit thathas an evaporator configured so that refrigerant flows in from below andflows out from above, wherein the control width is expanded when thecondensing ability of an evaporator is controlled by an expansion valve.

A refrigerating apparatus pertaining to a first invention comprises arefrigerant circuit and an oil returning circuit. The refrigerantcircuit is configured by the interconnection of a compression mechanism,a condenser, an expansion valve, and an evaporator configured so thatrefrigerant flows in from below and flows out from above, and uses acombination of refrigerating machine oil and refrigerant that does notseparate into two layers in a temperature range of 30° C. or below. Theoil returning circuit is connected to a lower portion of the evaporatorand returns the refrigerating machine oil accumulated inside theevaporator to the compression mechanism together with the refrigerant.

In this refrigerating apparatus, a refrigerant circuit having anevaporator configured so that refrigerant flows in from below and flowsout from above is provided, and a combination of refrigerating machineoil and refrigerant that does not separate into two layers in atemperature range of 30° C. or below is used as the refrigeratingmachine oil and refrigerant in the refrigerant circuit. Here, theevaporation temperature of the refrigerant in the evaporator is 30° C.or below when water, air, or brine is used as the heat source. For thisreason, in this refrigerating apparatus, the refrigerating machine oildoes not accumulate in a state where it floats on the surface of therefrigerant inside the evaporator, but rather accumulates inside theevaporator in a state where it is mixed with the refrigerant. Therefrigerating machine oil accumulated inside the evaporator is returnedto the compression mechanism together with the refrigerant by way of theoil returning circuit connected to the lower portion of the evaporator.For this reason, there is no longer a need to keep the surface of therefrigerant inside the heat source heat exchanger at a constant level orhigher in order to prevent the refrigerating machine oil fromaccumulating inside the evaporator, as is the case of conventionalrefrigerating apparatuses.

Thus, in this refrigerating apparatus, even if control is conducted toreduce the evaporating ability of the evaporator by reducing the openingof the expansion valve in accordance with the refrigerating load so thatas a result the level of the refrigerant inside the evaporator drops,the refrigerating machine oil does not accumulate inside the evaporator.For this reason, the control width when the evaporating ability of theevaporator is controlled by the expansion valve can be expanded.

A refrigerating apparatus pertaining to a second invention comprises therefrigerating apparatus pertaining to the first invention, wherein therefrigerating machine oil and refrigerant used in the refrigerantcircuit are a combination of refrigerating machine oil and refrigerantthat does not separate into two layers in a temperature range of −5° C.or below.

In this refrigerating apparatus, a combination of refrigerating machineoil and refrigerant that does not separate into two layers in atemperature range of −5° C. or below is used as the combination ofrefrigerating machine oil and refrigerant. For this reason, in thisrefrigerating apparatus, the refrigerating machine oil does notaccumulate in a state where it floats on the surface of the refrigerantinside the evaporator, but rather accumulates inside the evaporator in astate where it is mixed with the refrigerant. In this case as well, therefrigerating machine oil can be prevented from accumulating inside theevaporator.

A refrigerating apparatus pertaining to a third invention comprises therefrigerating apparatus pertaining to the second invention, wherein thecombination of refrigerating machine oil and refrigerant used in therefrigerant circuit is ethereal oil and R410A.

In this refrigerating apparatus, ethereal oil is used as therefrigerating machine oil, and R410A is used as the refrigerant. Withthis combination of refrigerating machine oil and refrigerant,separation into two layers does not occur in a temperature range of −5°C. or below. In this case as well, the refrigerating machine oil can beprevented from accumulating inside the evaporator.

A refrigerating apparatus pertaining to a fourth invention comprises therefrigerating apparatus pertaining to any of the first to thirdinventions, and further comprises a pressure difference increasingmechanism for increasing the pressure difference before the merging ofthe refrigerating machine oil and the refrigerant returned to thecompression mechanism from the lower portion of the heat source heatexchanger through the oil returning circuit.

In the refrigerating apparatuses of the first to third inventions, theflow rate of refrigerating machine oil and refrigerant returned to thecompression mechanism from the lower portion of the evaporator throughthe oil returning circuit is determined in the oil returning circuit inaccordance with the pressure loss between the lower portion of theevaporator and the compression mechanism. For this reason, in caseswhere, for example, the pressure loss inside the evaporator and insidethe pipe from the refrigerant outlet side of the heat source heatexchanger to the intake side of the compression mechanism is small andthe pressure loss in the oil returning circuit ends up becoming small,cases can arise where the refrigerating machine oil and the refrigerantof a flow rate sufficient enough to be able to prevent the refrigeratingmachine oil from accumulating inside the heat source heat exchangercannot be returned to the compression mechanism from the lower portionof the heat source heat exchanger through the oil returning circuit.

In this refrigerating apparatus, however, refrigerating machine oil andrefrigerant, which have a flow rate that is sufficient to preventrefrigerating machine oil from accumulating inside the evaporator, canbe reliably returned from the lower portion of the evaporator to thecompression mechanism by way of the oil returning circuit. This can beachieved because the flow rate of the refrigerating machine oil andrefrigerant returned from the lower portion of the evaporator to thecompression mechanism by way of the oil returning circuit can beincreased by providing a pressure difference increasing mechanism.

A refrigerating apparatus pertaining to a fifth invention comprises arefrigerant circuit and an oil returning circuit. The refrigerantcircuit is configured by the interconnection of a compression mechanism,condensers, an expansion valve, and an evaporator configured so thatrefrigerant flows in from below and flows out from above, and uses acombination of refrigerating machine oil and refrigerant that does notseparate into two layers in the evaporator. The oil returning circuit isconnected to a lower portion of the evaporator and returns therefrigerating machine oil accumulated inside the evaporator to thecompression mechanism together with the refrigerant.

In this refrigerating apparatus, a refrigerant circuit having anevaporator configured so that refrigerant flows in from below and flowsout from above is provided and a combination of refrigerating machineoil and refrigerant that does not separate into two layers in theevaporator is used as the refrigerating machine oil and refrigerant inthe refrigerant circuit. For this reason, in this refrigeratingapparatus, the refrigerating machine oil does not accumulate in a statewhere it floats on the surface of the refrigerant inside the evaporatorunder conditions corresponding to the evaporation temperature of therefrigerant in the evaporator, but rather accumulates inside theevaporator in a state where it is mixed with the refrigerant. Therefrigerating machine oil accumulated inside the evaporator is returnedto the compression mechanism together with the refrigerant by way of theoil returning circuit connected to the lower portion of the evaporator.For this reason, there is no longer a need to keep the surface of therefrigerant inside the heat source heat exchanger at a constant level orhigher in order to prevent the refrigerating machine oil fromaccumulating inside the evaporator, as is the case of conventionalrefrigerating apparatuses.

Thus, in this refrigerating apparatus, even if control is conducted toreduce the evaporating ability of the evaporator by reducing the openingof the expansion valve in accordance with the refrigerating load so thatas a result the level of the refrigerant inside the evaporator drops,the refrigerating machine oil does not accumulate inside the evaporator.For this reason, the control width when the evaporating ability of theevaporator is controlled by the expansion valve can be expanded.

An air conditioner pertaining to a sixth invention comprises arefrigerant circuit and an oil returning circuit. The refrigerantcircuit has a structure in which a plurality of utilization refrigerantcircuits configured by the interconnection of a utilization heatexchanger and a utilization expansion valve are connected to a heatsource refrigerant circuit configured by the interconnection of acompression mechanism, a heat source heat exchanger configured so thatrefrigerant flows in from below and flows out from above whenfunctioning as an evaporator, and a heat source expansion valve, and inwhich a combination of refrigerating machine oil and refrigerant thatdoes not separate into two layers in a temperature range of 30° C. orbelow is used. The oil returning circuit is connected to a lower portionof the heat source heat exchanger and returns the refrigerating machineoil accumulated inside the heat source heat exchanger to the compressionmechanism together with the refrigerant.

This air conditioner comprises a heat source refrigerant circuit havinga heat source heat exchanger configured so that the refrigerant flows infrom below and flows out from above, and a refrigerant circuitconfigured by the interconnection of a plurality of utilizationrefrigerant circuits. A combination of refrigerating machine oil andrefrigerant that does not separate into two layers in a temperaturerange of 30° C. or below is used as the refrigerating machine oil andrefrigerant in the refrigerant circuit. Here, the evaporationtemperature of the refrigerant in the heat source heat exchanger is 30°C. or below when water, air, or brine is used as the heat source. Forthis reason, in this air conditioner, the refrigerating machine oil doesnot accumulate in a state where it floats on the surface of therefrigerant inside the heat source heat exchanger, but ratheraccumulates inside the heat source heat exchanger in a state where it ismixed with the refrigerant. The refrigerating machine oil accumulatedinside the heat source heat exchanger is returned to the compressionmechanism together with the refrigerant by way of the oil returningcircuit connected to the lower portion of the heat source heatexchanger. For this reason, there is no longer a need to keep thesurface of the refrigerant inside the heat source heat exchanger at aconstant level or higher in order to prevent the refrigerating machineoil from accumulating inside the heat source heat exchanger, as is thecase of conventional air conditioners.

Therefore, in this air conditioner, even if control is conducted toreduce the evaporating ability of the heat source heat exchanger byreducing the opening of the heat source expansion valve in accordancewith the air conditioning load of the plurality of utilizationrefrigerant circuits so that as a result the level of the refrigerantinside the heat source heat exchanger drops, the refrigerating machineoil does not accumulate inside the heat source heat exchanger. For thisreason, the control width when the evaporating ability of the heatsource heat exchanger is controlled by the heat source expansion valvecan be expanded.

Additionally, in this air conditioner, it becomes unnecessary to conductcontrol, as in conventional air conditioners disposed with a pluralityof heat source heat exchangers, to reduce the evaporating ability byclosing some of the heat source expansion valves to reduce the number ofheat source heat exchangers functioning as evaporators when the heatsource heat exchangers are caused to function as evaporators or toreduce the evaporating ability by causing some of the heat source heatexchangers to function as condensers to offset the evaporating abilityof the heat source heat exchangers functioning as evaporators. For thisreason, a wide control width of the evaporating ability can be obtainedby a single heat source heat exchanger.

Thus, because simplification of the heat source heat exchanger becomespossible in an air conditioner where simplification of the heat sourceheat exchangers could not be realized by restricting the control widthof the control of the evaporating ability of the heat source heatexchangers, increases in the number of parts and cost that had occurredin conventional air conditioners as a result of disposing plural heatsource heat exchangers can be prevented. Further, the problem of the COPbecoming poor can be eliminated in an operating condition where, whensome of the heat source heat exchangers are caused to function ascondensers to reduce the evaporating ability, the amount of refrigerantcompressed in the compression mechanism increases in correspondence tothe amount of refrigerant condensed by the heat source heat exchangersand the air conditioning load of the utilization refrigerant circuits issmall.

An air conditioner pertaining to a seventh invention comprises the airconditioner pertaining to the sixth invention, wherein the refrigeratingmachine oil and refrigerant used in the refrigerant circuit are acombination of refrigerating machine oil and refrigerant that does notseparate into two layers in a temperature range of −5° C. or below.

In this refrigerating apparatus, a combination of refrigerating machineoil and refrigerant that does not separate into tow layers in atemperature range of −5° C. or below is used as the combination ofrefrigerating machine oil and refrigerant. For this reason, in thisrefrigerating apparatus, the refrigerating machine oil does notaccumulate in a state where it floats on the surface of the refrigerantinside the heat source heat exchanger, but rather accumulates inside theheat source heat exchanger in a state where it is mixed with therefrigerant, even when the evaporation temperature of the refrigerant islow in the heat source heat exchanger functioning as an evaporator. Inthis case as well, the refrigerating machine oil can be prevented fromaccumulating inside the heat source heat exchanger.

An air conditioner pertaining to an eighth invention comprises the airconditioner pertaining to the seventh invention, wherein the combinationof refrigerating machine oil and refrigerant used in the refrigerantcircuit is ethereal oil and R410A.

In this air conditioner, ethereal oil is used as the refrigeratingmachine oil, and R410A is used as the refrigerant. This combination ofrefrigerating machine oil and refrigerant does not separate into twolayers in a temperature range of −5° C. or below, and the refrigeratingmachine oil can therefore be prevented from accumulating inside the heatsource heat exchanger.

An air conditioner pertaining to a ninth invention comprises the airconditioner pertaining to any of the sixth to eighth inventions, andfurther comprises a pressure difference increasing mechanism forincreasing the pressure difference before the merging of therefrigerating machine oil and the refrigerant returned to thecompression mechanism from the lower portion of the heat source heatexchanger through the oil returning circuit.

In the air conditioner pertaining to any of the sixth to eighthinventions, the flow rate of refrigerating machine oil and refrigerantreturned to the compression mechanism from the lower portion of the heatsource heat exchanger functioning as an evaporator through the oilreturning circuit is determined in the oil returning circuit inaccordance with the pressure loss between the lower portion of the heatsource heat exchanger functioning as an evaporator and the compressionmechanism. For this reason, in cases where, for example, the pressureloss inside the heat source heat exchanger functioning as an evaporatorand inside the pipe from the refrigerant outlet side of the heat sourceheat exchanger to the intake side of the compression mechanism is smalland the pressure loss in the oil returning circuit ends up becomingsmall, cases can arise where the refrigerating machine oil and therefrigerant of a flow rate sufficient enough to be able to prevent therefrigerating machine oil from accumulating inside the heat source heatexchanger cannot be returned to the compression mechanism from the lowerportion of the heat source heat exchanger through the oil returningcircuit.

However, in this air conditioner, refrigerating machine oil andrefrigerant, which have a flow rate that is sufficient to preventrefrigerating machine oil from accumulating inside the evaporator, canbe reliably returned from the lower portion of the evaporator to thecompression mechanism by way of the oil returning circuit. This can beachieved because the flow rate of the refrigerating machine oil andrefrigerant returned from the lower portion of the evaporator to thecompression mechanism by way of the oil returning circuit can beincreased by providing a pressure difference increasing mechanism.

An air conditioner pertaining to a tenth invention comprises the airconditioner pertaining to any of the sixth to ninth inventions, whereinthe oil returning circuit has a control valve. The control valve isclosed when the heat source heat exchanger functions as a condenser, andis open when the heat source heat exchanger functions as an evaporator.

In this air conditioner, by disposing a control valve in the oilreturning circuit and adjusting the control value to a closed state whenthe heat source heat source heat exchanger is caused to function as acondenser, the flow rate of the refrigerant fed to the utilizationrefrigerant circuit can be prevented from being reduced after therefrigerant has been condensed in the heat source heat exchanger.

An air conditioner pertaining to an eleventh invention comprises the airconditioner pertaining to the tenth invention, wherein the control valveis opened when the heat source expansion valve is at or below aprescribed position.

In this air conditioner, it is not necessary to use the oil returningcircuit until the level of the refrigerant inside the heat source heatexchanger reaches a constant level or more where there is noaccumulation of refrigerating machine oil. For this reason, the openingof the heat source expansion valve corresponding to a level of therefrigerant where accumulation of the refrigerating machine oil canoccur inside the heat source heat exchanger 23 is set as a predeterminedopening, and the control valve is opened and the air conditioneroperates only when the opening of the heat source expansion valvebecomes equal to or less than this predetermined opening, whereby theamount of refrigerant sent to the compression mechanism can be preventedfrom increasing without the refrigerant being evaporated in the heatsource heat exchanger.

An air conditioner pertaining to a twelfth invention comprises the airconditioner pertaining to any of the sixth to eleventh inventions,wherein the heat source heat exchanger uses as a heat source water fedat a constant rate without regard to the flow rate of refrigerant thatflows inside the heat source heat exchanger.

In this air conditioner, the heat source heat exchanger uses as a heatsource water fed at a constant rate without regard to the flow rate ofrefrigerant that flows inside the heat source heat exchanger, and theevaporating ability in the heat source heat exchanger cannot becontrolled by controlling the amount of water. However, in this airconditioner, since the control width is expanded when the evaporatingability of the heat source heat exchanger is controlled by the heatsource expansion valve, the control width can be assured when theevaporating ability of the heat source heat exchanger is controlledwithout controlling the amount of water.

An air conditioner pertaining to a thirteenth invention comprises theair conditioner pertaining to any of the sixth to twelfth inventions,wherein the heat source heat exchanger is a plate heat exchanger.

In this air conditioner, a plate heat exchanger is used as the heatsource heat exchanger, and in terms of the structure thereof, it isdifficult for the refrigerating machine oil accumulating in a statewhere it floats on the surface of the refrigerant to be extracted fromthe vicinity of the surface of the refrigerant in order to prevent therefrigerating machine oil from accumulating inside the heat source heatexchanger. However, in this air conditioner, it suffices simply for therefrigerating machine oil to accumulate inside the heat source heatexchanger in a state where it is mixed with the refrigerant and for therefrigerating machine oil accumulating inside the heat source exchangerto be extracted from the lower portion of the heat source heat exchangertogether with the refrigerant. For this reason, it is easy to disposethe oil returning circuit even when a plate-type heat exchanger is used.

The air conditioner pertaining to a fourteenth invention has arefrigerant circuit and an oil returning circuit. The refrigerantcircuit has a structure in which a plurality of utilization refrigerantcircuits configured by the interconnection of a utilization heatexchanger and a utilization expansion valve are connected to a heatsource refrigerant circuit configured by the interconnection of acompression mechanism, a heat source heat exchanger configured so thatrefrigerant flows in from below and flows out from above when the heatsource heat exchanger functions as an evaporator, and a heat sourceexpansion valve; and uses a combination of refrigerating machine oil andrefrigerant that does not separate into two layers inside the heatsource heat exchanger when the heat source heat exchanger functions asan evaporator. The oil returning circuit is connected to a lower portionof the heat source heat exchanger and returns the refrigerating machineoil accumulated inside the heat source heat exchanger to the compressionmechanism together with the refrigerant.

In this air conditioner, a refrigerant circuit is provided thatconfigured by the interconnection a plurality of utilization refrigerantcircuits and a heat source refrigerant circuit having a heat source heatexchanger configured so that refrigerant flows in from below and flowsout from above when the heat source heat exchanger functions as anevaporator. Used as the refrigerating machine oil and refrigerant usedin the refrigerant circuit is a combination of refrigerating machine oiland refrigerant that does not separate into two layers inside the heatsource heat exchanger when the heat source heat exchanger functions asan evaporator. For this reason, in this air conditioner, therefrigerating machine oil does not accumulate in a state where it floatson the surface of the refrigerant inside the heat source heat exchangerunder conditions corresponding to the evaporation temperature of therefrigerant in the heat source heat exchanger functioning as anevaporator, but rather accumulates inside the heat source heat exchangerin a state where it is mixed with the refrigerant. The refrigeratingmachine oil accumulated in the heat source heat exchanger is returned tothe compression mechanism together with the refrigerant through the oilreturning circuit connected to the lower portion of the heat source heatexchanger. For this reason, there is no longer a need to keep thesurface of the refrigerant inside the heat source heat exchanger at aconstant level or higher in order to prevent the refrigerating machineoil from accumulating inside the heat source heat exchanger as is thecase of conventional air conditioners.

Thus, in this air conditioner, even when control is conducted to reducethe evaporating ability of the heat source heat exchanger by reducingthe opening of the heat source expansion valve in accordance with theair conditioning load of the plurality of utilization refrigerantcircuits so that as a result the level of the refrigerant inside theheat source heat exchanger drops, the refrigerating machine oil does notaccumulate inside the heat source heat exchanger. For this reason, thecontrol width when the evaporating ability of the heat source heatexchanger is controlled with a heat source expansion valve can beexpanded.

In this air conditioner, it becomes unnecessary to conduct control, asin conventional air conditioners disposed with plural heat source heatexchangers, to reduce the evaporating ability by closing some of theheat source expansion valves to reduce the number of heat source heatexchangers functioning as evaporators when the heat source heatexchangers are caused to function as evaporators or to reduce theevaporating ability by causing some of the heat source heat exchangersto function as condensers to offset the evaporating ability of the heatsource heat exchangers functioning as evaporators. For this reason, awide control width of the evaporating ability can be obtained by asingle heat source heat exchanger.

Thus, because simplification of the heat source heat exchanger becomespossible in an air conditioner where simplification of the heat sourceheat exchangers could not be realized by restricting the control widthof the control of the evaporating ability of the heat source heatexchangers, increases in the number of parts and cost that had occurredin conventional air conditioners as a result of disposing plural heatsource heat exchangers can be prevented. Further, the problem of the COPbecoming poor can be eliminated in an operating condition where, whensome of the heat source heat exchangers are caused to function ascondensers to reduce the evaporating ability, the amount of refrigerantcompressed in the compression mechanism increases in correspondence tothe amount of refrigerant condensed by the heat source heat exchangersand the air conditioning load of the entire plurality of utilizationrefrigerant circuits is small.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

A schematic diagram of a refrigerant circuit of an air conditioner of anembodiment pertaining to the invention.

FIG. 2

A diagram showing the overall schematic structure of a heat source heatexchanger.

FIG. 3

An enlarged view of portion C in FIG. 2 showing the schematic structureof a lower portion of the heat source heat exchanger.

FIG. 4

A schematic diagram of the refrigerant circuit describing the operationof the air conditioner during a heating operating mode.

FIG. 5

A schematic diagram of the refrigerant circuit describing the operationof the air conditioner during a cooling operating mode.

FIG. 6

A schematic diagram of the refrigerant circuit describing the operationof the air conditioner during a simultaneous cooling and heatingoperating mode (evaporation load).

FIG. 7

A schematic diagram of the refrigerant circuit describing the operationof the air conditioner during a simultaneous cooling and heatingoperating mode (condensation load).

FIG. 8

A schematic diagram of a refrigerant circuit of an air conditionerpertaining to modification 1.

FIG. 9

A schematic diagram of the refrigerant circuit describing the operationof the air conditioner of modification 1 during a heating operatingmode.

FIG. 10

A schematic diagram of the refrigerant circuit describing the operationof the air conditioner of modification 1 during a cooling operatingmode.

FIG. 11

A schematic diagram of a refrigerant circuit of an air conditionerpertaining to modification 2.

FIG. 12

A schematic diagram of a refrigerant circuit of an air conditionerpertaining to modification 3.

FIG. 13

A schematic diagram of a refrigerant circuit of an air conditionerpertaining to modification 4.

FIG. 14

A schematic diagram of the refrigerant circuit of the air conditionerpertaining to modification 4.

FIG. 15

A schematic diagram of the refrigerant circuit of the air conditionerpertaining to modification 4.

FIG. 16

A schematic diagram of the refrigerant circuit of the air conditionerpertaining to modification 4.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Air Conditioner (Refrigerating Apparatus)-   12 Refrigerant Circuit-   12 a, 12 b, 12 c Utilization Refrigerant Circuits-   12 d Heat Source Refrigerant Circuit-   21 Compression Mechanism-   23 Heat Source Heat Exchanger (Evaporator)-   24 Heat Source Expansion Valve (Expansion Valve)-   31, 41, 51 Utilization Expansion Valves-   32, 42, 52 Utilization Heat Exchangers (Condensers)-   101 First Oil Returning Circuit (Oil Returning Circuit)-   101 b Control Valve-   111 Pressurizing Circuit-   121 Cooler-   122 Cooling Circuit-   131, 141 Pressure-Reducing Mechanism (Pressure Difference Increasing    Mechanism)-   151 Pump Mechanism (Pressure Difference Increasing Mechanism)-   161 Ejector Mechanism (Pressure Difference Increasing Mechanism)

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of an air conditioner pertaining to the invention will bedescribed below on the basis of the drawings.

(1) Configuration of the Air Conditioner

FIG. 1 is a schematic diagram of a refrigerant circuit of an airconditioner 1 of an embodiment pertaining to the invention. The airconditioner 1 is an apparatus used to cool and heat the indoors ofbuildings and the like by conducting a vapor compression-typerefrigerating cycle.

The air conditioner 1 is mainly disposed with one heat source unit 2; aplurality of (three in the present embodiment) utilization units 3, 4and 5; connection units 6, 7 and 8 connected to the utilization units 3,4 and 5; and refrigerant communication pipes 9, 10 and 11 that connectthe heat source unit 2 and the utilization units 3, 4 and 5 via theconnection units 6, 7 and 8. The air conditioner 1 is configured suchthat it can conduct a simultaneous cooling and heating operation inaccordance with the requirements of indoor air conditioned spaces wherethe utilization units 3, 4 and 5 are disposed, such as conducting acooling operation in regard to a certain air conditioned space andconducting a heating operation in regard to another air conditionedspace, for example. That is, a vapor compression-type refrigerantcircuit 12 of the air conditioner 1 of the present embodiment isconfigured by the interconnection of the heat source unit 2, theutilization units 3, 4 and 5, the connection units 6, 7 and 8, and therefrigerant communication pipes 9, 10 and 11.

Additionally, in the present embodiment, a combination of refrigeratingmachine oil and refrigerant is used that does not separate into twolayers in a temperature range of −20° C. or below in the refrigerantcircuit 12 of the air conditioner 1. For example, a combination of R410Aand polyvinyl ether (PVE) or another ethereal oil is used as such acombination of refrigerant and refrigerating machine oil. Following arethe reasons for using a combination of refrigerating machine oil andrefrigerant that does not separate into two layers in a temperaturerange of −20° C. or below.

First, in view of the fact that the maximum value of the evaporationtemperature of the refrigerant is 30° C. when the heat source heatexchanger 23 (described later) of the heat source unit 2 is caused tofunction as an evaporator, the refrigerant and refrigerating machine oilaccumulated inside the heat source heat exchanger 23 are not allowed toseparate in at least a temperature range that is equal to or below themaximum value (i.e., 30° C.) of the evaporation temperature, and therefrigerating machine oil can thereby be extracted together with therefrigerant from the lower portion of the heat source heat exchanger 23and returned to the compression mechanism 21 (described later) of theheat source unit 2.

More preferably, in view of the minimum value of the evaporationtemperature of the refrigerant when the heat source heat exchanger 23(described later) of the heat source unit 2 is caused to function as anevaporator, the refrigerant and refrigerating machine oil accumulatedinside the heat source heat exchanger 23 are not allowed to separateinto two layers in a temperature range that is equal to or less than theminimum value of the evaporation temperature, whereby the refrigeratingmachine oil can be extracted together with the refrigerant from thelower portion of the heat source heat exchanger 23 and returned to thecompression mechanism 21 (described later) of the heat source unit 2.When water is used as the heat source of the 23, the minimum value ofthe evaporation temperature is −5° C. When air is used as the heatsource of the heat source heat exchanger 23, the minimum value of theevaporation temperature is −15° C. When brine (e.g., one that includes40 to 50 wt % ethylene glycol) is used as the heat source of the heatsource heat exchanger 23, the minimum value of the evaporationtemperature is −20° C.

<Utilization Units>

The utilization units 3, 4 and 5 are disposed such by being embedded inor hung from an indoor ceiling of a building or the like, or by beingmounted on an indoor wall. The utilization units 3, 4 and 5 areconnected to the heat source unit 2 via the refrigerant communicationpipes 9, 10 and 11 and the connection units 6, 7 and 8, and configurepart of the refrigerant circuit 12.

Next, the configuration of the utilization units 3, 4 and 5 will bedescribed. It will be noted that because the utilization unit 3 has thesame configuration as those of the utilization units 4 and 5, just theconfiguration of the utilization unit 3 will be described here, and inregard to the configurations of the utilization units 4 and 5, referencenumerals in the 40 s and 50 s will be used instead of reference numeralsin the 30 s representing the respective portions of the utilization unit3, and description of those respective portions will be omitted.

The utilization unit 3 mainly configures part of the refrigerant circuit12 and is disposed with a utilization refrigerant circuit 12 a (in theutilization units 4 and 5, utilization refrigerant circuits 12 b and 12c). The utilization refrigerant circuit 12 a is mainly disposed with autilization expansion valve 31 and a utilization heat exchanger 32. Inthe present embodiment, the utilization expansion valve 31 is anelectrically powered expansion valve connected to a liquid side of theutilization heat exchanger 32 in order to regulate the flow rate of therefrigerant flowing inside the utilization refrigerant circuit 12 a. Inthe present embodiment, the utilization heat exchanger 32 is a crossfin-type fin-and-tube heat exchanger configured by a heat transfer tubeand numerous fins, and is a device for conducting heat exchange betweenthe refrigerant and the indoor air. In the present embodiment, theutilization unit 3 is disposed with a blower fan (not shown) for takingin indoor air to the inside of the unit, heat-exchanging the air, andthereafter supplying the air to the indoors as supply air, so that theindoor air and the refrigerant flowing through the utilization heatexchanger 32 can be heat-exchanged.

Various types of sensors are also disposed in the utilization unit 3. Aliquid temperature sensor 33 that detects the temperature of liquidrefrigerant is disposed at the liquid side of the utilization heatexchanger 32, and a gas temperature sensor 34 that detects thetemperature of gas refrigerant is disposed at a gas side of theutilization heat exchanger 32. Moreover, an RA intake temperature sensor35 that detects the temperature of the indoor air taken into the unit isdisposed in the utilization unit 3. Further, the utilization unit 3 isdisposed with a utilization control unit 36 that controls the operationof the respective portions configuring the utilization unit 3.Additionally, the utilization control unit 36 is disposed with amicrocomputer and memory disposed in order to control the utilizationunit 3, and is configured such that it can exchange control signals andthe like with a remote controller (not shown) and exchange controlsignals and the like with the heat source unit 2.

<Heat Source Unit>

The heat source unit 2 is disposed on the roof or the like of a buildingor the like, is connected to the utilization units 3, 4 and 5 via therefrigerant communication pipes 9, 10 and 11, and configures therefrigerant circuit 12 between the utilization units 3, 4 and 5.

Next, the configuration of the heat source unit 2 will be described. Theheat source unit 2 mainly configures part of the refrigerant circuit 12and is disposed with a heat source refrigerant circuit 12 d. The heatsource refrigerant circuit 12 d is mainly disposed with the compressionmechanism 21, a first switch mechanism 22, the heat source heatexchanger 23, a heat source expansion valve 24, a receiver 25, a secondswitch mechanism 26, a liquid closing valve 27, a high-pressure gasclosing valve 28, a low-pressure gas closing valve 29, a first oilreturning circuit 101, a pressurizing circuit 111, a cooler 121, and acooling circuit 122.

The compression mechanism 21 mainly includes a compressor 21 a, an oilseparator 21 b connected to a discharge side of the compressor 21 a, anda second oil returning circuit 21 d that connects the oil separator 21 band an intake pipe 21 c of the compressor 21 a. In the presentembodiment, the compressor 21 a is a positive-displacement compressorwhose running capacity can be varied by inverter control. The oilseparator 21 b is a container that separates the refrigerating machineoil accompanying the high-pressure gas refrigerant compressed anddischarged in the compressor 21 a. The second oil returning circuit 21 dis a circuit for returning the refrigerating machine oil separated inthe oil separator 21 b to the compressor 21 a. The second oil returningcircuit 21 d mainly includes an oil returning pipe 21 e, which connectsthe oil separator 21 b and the intake pipe 21 c of the compressor 21 a,and a capillary tube 21 f, which reduces the pressure of thehigh-pressure refrigerating machine oil separated in the oil separator21 b connected to the oil returning pipe 21 e. The capillary tube 21 fis a narrow tube that reduces, to the refrigerant pressure of the intakeside of the compressor 21 a, the pressure of the high-pressurerefrigerating machine oil separated in the oil separator 21 b. In thepresent embodiment, the compression mechanism 21 only has the onecompressor 21 a but is not limited thereto, and may also be one wheretwo or more compressors are connected in parallel in accordance with theconnection number of utilization units.

The first switch mechanism 22 is a four-way switch valve that can switchbetween flow paths of the refrigerant inside the heat source refrigerantcircuit 12 d such that when the heat source heat exchanger 23 is causedto function as a condenser (below, referred to as a condensationoperating state), the first switch mechanism 22 connects the dischargeside of the compression mechanism 21 and the gas side of the heat sourceheat exchanger 23, and when the heat source heat exchanger 23 is causedto function as an evaporator (below, referred to as an evaporationoperating state), the first switch mechanism 22 connects the intake sideof the compression mechanism 21 and the gas side of the heat source heatexchanger 23. A first port 22 a of the first switch mechanism 22 isconnected to the discharge side of the compression mechanism 21, asecond port 22 b of the first switch mechanism 22 is connected to thegas side of the heat source heat exchanger 23, a third port 22 c of thefirst switch mechanism 22 is connected to the intake side of thecompression mechanism 21, and a fourth port 22 d of the first switchmechanism 22 is connected to the intake side of the compressionmechanism 21 via a capillary tube 91. Additionally, as mentionedpreviously, the first switch mechanism 22 can conduct switching thatconnects the first port 22 a and the second port 22 b and connects thethird port 22 c and the fourth port 22 d (corresponding to thecondensation operating state; refer to the solid lines of the firstswitch mechanism 22 in FIG. 1), and connects the second port 22 b andthe third port 22 c and connects the first port 22 a and the fourth port22 d (corresponding to the evaporation operating state; refer to thedotted lines of the first switch mechanism 22 in FIG. 1).

The heat source heat exchanger 23 is a heat exchanger that can functionas an evaporator of the refrigerant and as a condenser of therefrigerant. In the present embodiment, the heat source heat exchanger23 is a plate heat exchanger that exchanges heat with the refrigerantusing water as the heat source. The gas side of the heat source heatexchanger 23 is connected to the second port 22 b of the first switchmechanism 22, and the liquid side of the heat source heat exchanger 22is connected to the heat source expansion valve 24. As shown in FIG. 2,the heat source heat exchanger 23 is configured such that it can conductheat exchange as a result of plural plate members 23 a formed bypressing or the like being superposed via packing (not shown) so thatplural flow paths 23 b and 23 c extending in the vertical direction areformed between the plate members 23 a, whereby the refrigerant and wateralternately flow inside these plural flow paths 23 b and 23 c(specifically, the refrigerant flows inside the flow paths 23 b and thewater flows inside the flow paths 23 c; refer to arrows A and B in FIG.2). Additionally, the plural flow paths 23 b are mutually communicatedat their upper end portions and lower end portions, and are connected toa gas nozzle 23 d and a liquid nozzle 23 e disposed on the upper portionand the lower portion of the heat source heat exchanger 23. The gasnozzle 23 d is connected to the first switch mechanism 22, and theliquid nozzle 23 e is connected to the heat source expansion valve 24.Thus, as shown by arrow A in FIG. 2, when the heat source heat exchanger23 functions as an evaporator, the refrigerant flows in from the liquidnozzle 23 e (i.e., from below) and flows out from the gas nozzle 23 d(i.e., from above), and when the heat source heat exchanger 23 functionsas a condenser, the refrigerant flows in from the gas nozzle 23 d (i.e.,from above) and flows out from the liquid nozzle 23 e (i.e., frombelow). Further, the plural flow paths 23 c are mutually communicated attheir upper end portions and lower end portions, and are connected to awater inlet nozzle 23 f and a water outlet nozzle 23 g disposed on theupper portion and the lower portion of the heat source heat exchanger23. Further, in the present embodiment, the water serving as the heatsource flows in as supply water CWS from the water inlet nozzle 23 f ofthe heat source heat exchanger 23 through a water pipe (not shown) froma cooling tower facility or a boiler facility disposed outside the airconditioner 1, is heat-exchanged with the refrigerant, flows out fromthe water outlet nozzle 23 g, and is returned as discharge water CWR tothe cooling tower facility or the boiler facility. Here, a constantamount of the water supplied from the cooling tower facility or theboiler facility is supplied without relation to the flow rate of therefrigerant flowing inside the heat source heat exchanger 23.

In the present embodiment, the heat source expansion valve 24 is anelectrically powered expansion valve that can regulate the flow rate ofthe refrigerant flowing between the heat source heat exchanger 23 andthe utilization refrigerant circuits 12 a, 12 b and 12 c via the liquidrefrigerant communication pipe 9, and is connected to the liquid side ofthe heat source heat exchanger 23.

The receiver 25 is a container for temporarily accumulating therefrigerant flowing between the heat source heat exchanger 23 and theutilization refrigerant circuits 12 a, 12 b and 12 c. In the presentembodiment, the receiver 25 is connected between the heat sourceexpansion valve 24 and the cooler 121.

The second switch mechanism 26 is a four-way switch valve that canswitch between the flow paths of the refrigerant inside the heat sourcerefrigerant circuit 12 d such that when the heat source unit 2 is usedas a heat source unit for a simultaneous cooling and heating machine(refer to FIGS. 4 to 7) and sends the high-pressure gas refrigerant tothe utilization refrigerant circuits 12 a, 12 b and 12 c (below,referred to as a heating load requirement operating state), the secondswitch mechanism 26 connects the discharge side of the compressionmechanism 21 and the high-pressure gas closing valve 28, and when theheat source unit 2 is used as a heat source unit for a cooling andheating switching machine (modification 1; refer to FIGS. 8 to 10;below, referred to as a cooling/heating switching time cooling operatingstate) to conduct a cooling operation, the second switch mechanism 26connects the high-pressure gas closing valve 28 and the intake side ofthe compression mechanism 21. A first port 26 a of the second switchmechanism 26 is connected to the discharge side of the compressionmechanism 21, a second port 26 b of the second switch mechanism 26 isconnected to the intake side of the compression mechanism 21 via acapillary tube 92, a third port 26 c of the second switch mechanism 26is connected to the intake side of the compression mechanism 21, and afourth port 26 d of the second switch mechanism 26 is connected to thehigh-pressure gas closing valve 28. Additionally, as mentionedpreviously, the second switch mechanism 26 can conduct switching thatconnects the first port 26 a and the second port 26 b and connects thethird port 26 c and the fourth port 26 d (corresponding to thecooling/heating switching time cooling operating state; refer to thesolid lines of the second switch mechanism 26 in FIG. 1), and connectsthe second port 26 b and the third port 26 c and connects the first port26 a and the fourth port 26 d (corresponding to the heating loadrequirement operating state; refer to the dotted lines of the secondswitch mechanism 26 in FIG. 1).

The liquid closing valve 27, the high-pressure gas closing valve 28 andthe low-pressure gas closing valve 29 are valves disposed at portsconnected to external devices/pipes (specifically, the refrigerantcommunication pipes 9, 10 and 11). The liquid closing valve 27 isconnected to the cooler 121. The high-pressure gas closing valve 28 isconnected to the fourth port 26 d of the second switch mechanism 26. Thelow-pressure gas closing valve 29 is connected to the intake side of thecompression mechanism 21.

The first oil returning circuit 101 is a circuit that returns therefrigerating machine oil accumulating inside the heat source heatexchanger 23 to the compression mechanism 21 together with therefrigerant during the evaporation operating state, i.e., when the heatsource heat exchanger 23 is caused to function as an evaporator. Thefirst oil returning circuit 101 mainly includes an oil returning pipe101 a that connects the lower portion of the heat source heat exchanger23 and the compression mechanism 21, a control valve 101 b connected tothe oil returning pipe 101 a, a check valve 101 c, and a capillary tube101 d. The oil returning pipe 101 a is disposed such that one end canextract the refrigerating machine oil together with the refrigerant fromthe lower portion of the heat source heat exchanger 23. In the presentembodiment, as shown in FIG. 3, the oil returning pipe 101 a is a pipeextending inside the flow paths 23 b through which flows the refrigerantof the heat source heat exchanger 23 through the inside of the pipe ofthe liquid nozzle 23 e disposed in the lower portion of the heat sourceheat exchanger 23. Here, communication holes 23 h are disposed in theplate members 23 a in the heat source heat exchanger 23 in order toallow the plural flow paths 23 b to be communicated with each other (thesame is true of the plural flow paths 23 c). For this reason, the oilreturning pipe 101 a may also be disposed such that it penetrates theplural flow paths 23 b (refer to the oil returning pipe 101 a indicatedby the dotted lines in FIG. 3). Further, in the present embodiment, theother end of the oil returning pipe 101 a is connected to the intakeside of the compression mechanism 21. In the present embodiment, thecontrol valve 101 b is an electromagnetic valve that is connected toensure that it can use the first oil returning circuit 101 as needed,and can circulate and cut off the refrigerant and the refrigeratingmachine oil. The check valve 101 c is a valve that allows therefrigerant and the refrigerating machine oil to flow just inside theoil returning pipe 101 a toward the intake side of the compressionmechanism 21 from the lower portion of the heat source heat exchanger23. The capillary tube 101 d is a narrow tube that reduces, to therefrigerant pressure of the intake side of the compression mechanism 21,the pressure of the refrigerant and the refrigerating machine oilextracted from the lower portion of the heat source heat exchanger 23.

The pressurizing circuit 111 is a circuit that causes the high-pressuregas refrigerant compressed in the compression mechanism 21 to merge withthe refrigerant that is condensed in the heat source heat exchanger 23,pressure-reduced in the heat source expansion valve 24, and sent to theutilization refrigerant circuits 12 a, 12 b and 12 c during thecondensation operating state, i.e., when the heat source heat exchanger23 is caused to function as a condenser. The pressurizing circuit 111mainly includes a pressurizing pipe 111 a that connects the dischargeside of the compression mechanism 21 and the downstream side of the heatsource expansion valve 24 (i.e., between the heat source expansion valve24 and the liquid closing valve 27), a control valve 111 b connected tothe pressurizing pipe 111 a, a check valve 111 c, and a capillary tube111 d. In the present embodiment, one end of the pressurizing pipe 111 ais connected between the outlet of the oil separator 21 b of thecompression mechanism 21 and the first ports 22 a and 26 a of the firstand second switch mechanisms 22 and 26. Further, in the presentembodiment, the other end of the pressurizing pipe 111 a is connectedbetween the heat source expansion valve 24 and the receiver 25. In thepresent embodiment, the control valve 111 b is an electromagnetic valvethat is connected to ensure that it can use the pressurizing circuit 111as needed, and can circulate and cut off the refrigerant. The checkvalve 111 c is a valve that allows the refrigerant to flow just insidethe pressurizing pipe 111 a toward the downstream side of the heatsource expansion valve 24 from the discharge side of the compressionmechanism 21. The capillary tube 111 d is a narrow tube that reduces, tothe refrigerant pressure of the downstream side of the heat sourceexpansion valve 24, the pressure of the refrigerant extracted from thedischarge side of the compression mechanism 21.

The cooler 121 is a heat exchanger that cools the refrigerant that iscondensed in the heat source heat exchanger 23, pressure-reduced in theheat source expansion valve 24, and sent to the utilization refrigerantcircuits 12 a, 12 b and 12 c during the condensation operating state,i.e., when the heat source heat exchanger 23 is caused to function as acondenser. In the present embodiment, the cooler 121 is connectedbetween the receiver 25 and the liquid closing valve 27. In other words,the pressurizing circuit 111 is connected such that the pressurizingpipe 111 a is connected between the heat source expansion valve 24 andthe cooler 121, so that the high-pressure gas refrigerant merges withthe refrigerant whose pressure has been reduced in the heat sourceexpansion valve 24. A double tube heat exchanger, for example, can beused as the cooler 121.

The cooling circuit 122 is a circuit connected to the heat sourcerefrigerant circuit 12 d such that during the condensation operatingstate, i.e., when the heat source heat exchanger 23 is caused tofunction as a condenser, the cooling circuit 122 causes some of therefrigerant sent from the heat source heat exchanger 23 to theutilization refrigerant circuits 12 a, 12 b and 12 c to branch from theheat source refrigerant circuit 12 d and be introduced to the cooler121, cools the refrigerant that is condensed in the heat source heatexchanger 23, pressure-reduced in the heat source expansion valve 24,and sent to the utilization refrigerant circuits 12 a, 12 b and 12 c,and returns the refrigerant to the intake side of the compressionmechanism 21. The cooling circuit 122 mainly includes a lead-in pipe 122a that introduces to the cooler 121 some of the refrigerant sent fromthe heat source heat exchanger 23 to the utilization refrigerantcircuits 12 a, 12 b and 12 c, a cooling circuit expansion valve 122 bconnected to the lead-in pipe 122 a, and a lead-out pipe 122 c thatreturns, to the intake side of the compression mechanism 21, therefrigerant passing through the cooler 121. In the present embodiment,one end of the lead-in pipe 122 a is connected between the receiver 25and the cooler 121. Further, in the present embodiment, the other end ofthe lead-in pipe 122 a is connected to the inlet of the cooling circuit122 side of the cooler 121. In the present embodiment, the coolingcircuit expansion valve 122 b is an electrically powered expansion valvethat is connected to ensure that it can use the cooling circuit 122 asneeded, and can regulate the flow rate of the refrigerant flowingthrough the cooling circuit 122. In the present embodiment, one end ofthe lead-out pipe 122 c is connected to the outlet of the coolingcircuit 122 side of the cooler 121. Further, in the present embodiment,the other end of the lead-out pipe 122 c is connected to the intake sideof the compression mechanism 21.

Further, various types of sensors are disposed in the heat source unit2. Specifically, the heat source unit 2 is disposed with an intakepressure sensor 93 that detects the intake pressure of the compressionmechanism 21, a discharge pressure sensor 94 that detects the dischargepressure of the compression mechanism 21, a discharge temperature sensor95 that detects the discharge temperature of the refrigerant of thedischarge side of the compression mechanism 21, and a cooling circuitoutlet temperature sensor 96 that detects the temperature of therefrigerant flowing through the lead-out pipe 122 c of the coolingcircuit 122. Further, the heat source unit 2 is disposed with a heatsource control unit 97 that controls the operation of the respectiveportions configuring the heat source unit 2. Additionally, the heatsource control unit 97 includes a microcomputer and a memory disposed inorder to control the heat source unit 2, and is configured such that itcan exchange control signals and the like with the utilization controlunits 36, 46 and 56 of the utilization units 3, 4 and 5.

<Connection Units>

The connection units 6, 7 and 8 are disposed together with theutilization units 3, 4 and 5 inside the room of a building or the like.The connection units 6, 7 and 8 are intervened between the utilizationunits 3, 4 and 5 and the heat source unit 2 together with therefrigerant communication pipes 9, 10 and 11, and configure part of therefrigerant circuit 12.

Next, the configuration of the connection units 6, 7 and 8 will bedescribed. It will be noted that because the connection unit 6 has thesame configuration as those of the connection units 7 and 8, just theconfiguration of the connection unit 6 will be described here, and inregard to the configurations of the connection units 7 and 8, referencenumerals in the 70 s and 80 s will be used instead of reference numeralsin the 60 s representing the respective portions of the connection unit6, and description of those respective portions will be omitted.

The connection unit 6 mainly configures part of the refrigerant circuit12 and is disposed with a connection refrigerant circuit 12 e (in theconnection units 7 and 8, connection refrigerant circuits 12 f and 12 g,respectively). The connection refrigerant circuit 12 e mainly includes aliquid connection pipe 61, a gas connection pipe 62, a high-pressure gascontrol valve 66, and a low-pressure gas control valve 67. In thepresent embodiment, the liquid connection pipe 61 connects the liquidrefrigerant communication pipe 9 and the utilization expansion valve 31of the utilization refrigerant circuit 12 a. The gas connection pipe 62includes a high-pressure gas connection pipe 63 connected to thehigh-pressure gas refrigerant communication pipe 10, a low-pressure gasconnection pipe 64 connected to the low-pressure gas refrigerantcommunication pipe 11, and a junction gas connection pipe 65 that mergesthe high-pressure gas connection pipe 63 and the low-pressure gasconnection pipe 64. The junction gas connection pipe 65 is connected tothe gas side of the utilization heat exchanger 32 of the utilizationrefrigerant circuit 12 a. Additionally, in the present embodiment, thehigh-pressure gas control valve 66 is an electromagnetic valve that isconnected to the high-pressure gas connection pipe 63 and can circulateand cut off the refrigerant. In the present embodiment, the low-pressuregas control valve 67 is an electromagnetic valve that is connected tothe low-pressure gas connection pipe 64 and can circulate and cut offthe refrigerant. Thus, when the utilization unit 3 conducts the coolingoperation, the connection unit 6 can function to close the high-pressuregas control valve 66 and open the low-pressure gas control valve 67 suchthat the refrigerant flowing into the liquid connection pipe 61 throughthe liquid refrigerant communication pipe 9 is sent to the utilizationexpansion valve 31 of the utilization refrigerant circuit 12 a,pressure-reduced by the utilization expansion valve 31, evaporated inthe utilization heat exchanger 32, and thereafter returned to thelow-pressure gas refrigerant communication pipe 11 through the junctiongas connection pipe 65 and the low-pressure gas connection pipe 64.Further, when the utilization unit 3 conducts the heating operation, theconnection unit 6 can function to close the low-pressure gas controlvalve 67 and open the high-pressure gas control valve 66 such that therefrigerant flowing into the high-pressure gas connection pipe 63 andthe junction gas connection pipe 65 through the high-pressure gasrefrigerant communication pipe 10 is sent to the gas side of theutilization heat exchanger 32 of the utilization refrigerant circuit 12a, condensed in the utilization heat exchanger 32, pressure-reduced bythe utilization expansion valve 31, and thereafter returned to theliquid refrigerant communication pipe 9 through the liquid connectionpipe 61. Further, the connection unit 6 is disposed with a connectioncontrol unit 68 that controls the operation of the respective portionsconfiguring the connection unit 6. Additionally, the connection controlunit 68 includes a microcomputer and a memory disposed in order tocontrol the connection unit 6, and is configured such that it canexchange control signals and the like with the utilization control unit36 of the utilization unit 3.

As described above, the refrigerant circuit 12 of the air conditioner 1is configured by the interconnection of the utilization refrigerantcircuits 12 a, 12 b and 12 c, the heat source refrigerant circuit 12 d,the refrigerant communication pipes 9, 10 and 11, and the connectionrefrigerant circuits 12 e, 12 f and 12 g. Additionally, the airconditioner 1 of the present embodiment can conduct a simultaneouscooling and heating operation, such as the utilization unit 5 conductinga heating operation while the utilization units 3 and 4 conduct acooling operation, for example.

Additionally, in the air conditioner 1 of the present embodiment, aswill be described later, the control width is expanded when theevaporating ability of the heat source heat exchanger 23 is controlledby the heat source expansion valve 24 by using the first oil returningcircuit 101 when the heat source heat exchanger 23 is caused to functionas an evaporator, so that a wide control width of the evaporatingability can be obtained by the single heat source heat exchanger 23.Further, in the air conditioner 1, as will be described later, thecontrol width when the condensing ability of the heat source heatexchanger 23 is controlled by the heat source expansion valve 24 isexpanded by using the pressurizing circuit 111 and the cooler 121 whenthe heat source heat exchanger 23 is caused to function as a condenser,so that a wide control width of the condensing ability can be obtainedby the single heat source heat exchanger 23. Thus, in the airconditioner 1 of the present embodiment, simplification of the heatsource heat exchanger, which had been plurally disposed in conventionalair conditioners, is realized.

(2) Operation of the Air Conditioner

Next, the operation of the air conditioner 1 of the present embodimentwill be described.

The operating modes of the air conditioner 1 of the present embodimentcan be divided in accordance with the air conditioning load of each ofthe utilization units 3, 4 and 5 into a heating operating mode where allof the utilization units 3, 4 and 5 conduct the heating operation, acooling operating mode where all of the utilization units 3, 4 and 5conduct the cooling operation, and a simultaneous cooling and heatingoperating mode where some of the utilization units 3, 4 and 5 conductthe cooling operation while the other utilization units conduct theheating operation. Further, in regard to the simultaneous cooling andheating operating mode, the operating mode can be divided by the overallair conditioning load of the utilization units 3, 4 and 5 into when theheat source heat exchanger 23 of the heat source unit 2 is caused tofunction and operate as an evaporator (evaporation operating state) andwhen the heat source heat exchanger 23 of the heat source unit 2 iscaused to function and operate as a condenser (condensation operatingstate).

The operation of the air conditioner 1 in the four operating modes willbe described below.

<Heating Operating Mode>

When all of the utilization units 3, 4 and 5 conduct the heatingoperation, the refrigerant circuit 12 of the air conditioner 1 isconfigured as shown in FIG. 4 (refer to the arrows added to therefrigerant circuit 12 in FIG. 4 for the flow of the refrigerant).Specifically, in the heat source refrigerant circuit 12 d of the heatsource unit 2, the first switch mechanism 22 is switched to theevaporation operating state (the state indicated by the dotted lines ofthe first switch mechanism 22 in FIG. 4) and the second switch mechanism26 is switched to the heating load requirement operating state (thestate indicated by the dotted lines of the second switch mechanism 26 inFIG. 4), whereby the heat source heat exchanger 23 is caused to functionas an evaporator such that the high-pressure gas refrigerant compressedand discharged in the compression mechanism 21 can be supplied to theutilization units 3, 4 and 5 through the high-pressure gas refrigerantcommunication pipe 10. Further, the opening of the heat source expansionvalve 24 is regulated to reduce the pressure of the refrigerant. It willbe noted that the control valve 111 b of the pressurizing circuit 111and the cooling circuit expansion valve 122 b of the cooling circuit 122are closed so that the high-pressure gas refrigerant is caused to mergewith the refrigerant flowing through the heat source expansion valve 24and the receiver 25, the supply of the cooling source to the cooler 121is shut off, and the refrigerant flowing between the receiver 25 and theutilization units 3, 4 and 5 is not cooled. In the connection units 6, 7and 8, the low-pressure gas control valves 67, 77 and 87 are closed andthe high-pressure gas control valves 66, 76 and 86 are opened, wherebythe utilization heat exchangers 32, 42 and 52 of the utilization units3, 4 and 5 are caused to function as condensers. In the utilizationunits 3, 4 and 5, the openings of the utilization expansion valves 31,41 and 51 are regulated in accordance with the heating load of eachutilization unit, such as the openings being regulated on the basis ofthe degree of subcooling of the utilization heat exchangers 32, 42 and52 (specifically, the temperature difference between the refrigeranttemperature detected by the liquid temperature sensors 33, 43 and 53 andthe refrigerant temperature detected by the gas temperature sensors 34,44 and 54), for example.

In this configuration of the refrigerant circuit 12, a large portion ofthe refrigerating machine oil accompanying the high-pressure gasrefrigerant that has been compressed and discharged by the compressor 21a of the compression mechanism 21 is separated in the oil separator 21b, and the high-pressure gas refrigerant is sent to the second switchmechanism 26. Then, the refrigerating machine oil separated in the oilseparator 21 b is returned to the intake side of the compressor 21 athrough the second oil returning circuit 21 d. The high-pressure gasrefrigerant sent to the second switch mechanism 26 is sent to thehigh-pressure gas refrigerant communication pipe 10 through the firstport 26 a and the fourth port 26 d of the second switch mechanism 26 andthe high-pressure gas closing valve 28.

Then, the high-pressure gas refrigerant sent to the high-pressure gasrefrigerant communication pipe 10 is branched into three and sent to thehigh-pressure gas connection pipes 63, 73 and 83 of the connection units6, 7 and 8. The high-pressure gas refrigerant sent to the high-pressuregas connection pipes 63, 73 and 83 of the connection units 6, 7 and 8 issent to the utilization heat exchangers 32, 42 and 52 of the utilizationunits 3, 4 and 5 through the high-pressure gas control valves 66, 76 and86.

Then, the high-pressure gas refrigerant sent to the utilization heatexchangers 32, 42 and 52 is condensed in the utilization heat exchangers32, 42 and 52 of the utilization units 3, 4 and 5 as a result of heatexchange being conducted with the indoor air. The indoor air is heatedand supplied to the indoors. The refrigerant condensed in theutilization heat exchangers 32, 42 and 52 passes through the utilizationexpansion valves 31, 41 and 51 and is thereafter sent to the liquidconnection pipes 61, 71 and 81 of the connection units 6, 7 and 8.

Then, the refrigerant sent to the liquid connection pipes 61, 71 and 81is sent to the liquid refrigerant communication pipe 9 and merges.

Then, the refrigerant that has been sent to the liquid refrigerantcommunication pipe 9 and merged is sent to the receiver 25 through theliquid closing valve 27 and the cooler 121 of the heat source unit 2.The refrigerant sent to the receiver 25 is temporarily accumulatedinside the receiver 25, and the pressure of the refrigerant isthereafter reduced by the heat source expansion valve 24. Then, therefrigerant whose pressure has been reduced by the heat source expansionvalve 24 is evaporated in the heat source heat exchanger 23 as a resultof heat exchange being conducted with water serving as a heat source,becomes low-pressure gas refrigerant, and is sent to the first switchmechanism 22. Then, the low-pressure gas refrigerant sent to the firstswitch mechanism 22 is returned to the intake side of the compressionmechanism 21 through the second port 22 b and the third port 22 c of thefirst switch mechanism 22. In this manner, the operation in the heatingoperating mode is conducted.

At this time, there are cases where the heating loads of the utilizationunits 3, 4 and 5 become extremely small. In such cases, it is necessaryto reduce the refrigerant evaporating ability in the heat source heatexchanger 23 of the heat source unit 2 and balance the overall heatingload of the utilization units 3, 4 and 5 (specifically, the condensationloads of the utilization heat exchangers 32, 42 and 52). For thisreason, control is conducted to reduce the evaporation amount of therefrigerant in the heat source heat exchanger 23 by conducting controlto reduce the opening of the heat source expansion valve 24. Whencontrol is conducted to reduce the opening of the heat source expansionvalve 24, the level of the refrigerant inside the heat source heatexchanger 23 drops. Thus, in a heat exchanger configured such that therefrigerant flows in from below and flows out from above when the heatexchanger functions as an evaporator of the refrigerant (see FIG. 2 andFIG. 3), like the heat source heat exchanger 23 of the presentembodiment, it becomes difficult for the refrigerating machine oil to bedischarged together with the evaporated refrigerant, and it becomes easyfor accumulation of the refrigerating machine oil to occur.

However, in the air conditioner 1 of the present embodiment, acombination of refrigerating machine oil and refrigerant that does notseparate into two layers in a temperature range of 30° C. or below (morepreferably, the minimum value of the evaporation temperature or less) isused (i.e., a combination of refrigerating machine oil and refrigerantthat does not separate into two layers in the heat source heat exchangerwhen the heat source heat exchanger functions as an evaporator), and thefirst oil returning circuit 101 is disposed. Additionally, the controlvalve 101 b of the first oil returning circuit 101 is configured to beopened during the heating operating mode (i.e., when the first switchmechanism 22 is in the evaporation operating state) such that it canextract, and return to the compression mechanism 21, the refrigeratingmachine oil together with the refrigerant from the inside of the heatsource heat exchanger 23 from the lower portion of the heat source heatexchanger 23 through the oil returning pipe 101 a. For this reason, eventhough the level of the refrigerant inside the heat source heatexchanger 23 drops as a result of control being conducted to reduce theopening of the heat source expansion valve 24 and it becomes difficultfor the refrigerating machine oil to be discharged together with theevaporated refrigerant, accumulation of the refrigerating machine oilinside the heat source heat exchanger 23 can be prevented.

It will be noted that it is preferable for the control valve 101 b to beclosed when the first switch mechanism 22 is in the condensationoperating state and to be opened when the first switch mechanism 22 isin the evaporation operating state because when the control valve 101 bis opened when the heat source heat exchanger 23 functions as acondenser, some of the refrigerant condensed in the heat source heatexchanger 23 is returned to the compression mechanism 21 and the amountof refrigerant sent to the utilization refrigerant circuits 12 a, 12 band 12 c is reduced. Moreover, the control valve 101 b may also beconfigured such that when the first switch mechanism 22 is in theevaporation operating state, the control valve 101 b is opened only whenthe level of the refrigerant inside the heat source heat exchanger 23drops as a result of control being conducted to reduce the opening ofthe heat source expansion valve 24 and it becomes difficult for therefrigerating machine oil to be discharged together with the evaporatedrefrigerant. For example, the conditions under which the control valve101 b is opened may be when the first switch mechanism 22 is in theevaporation operating state and when the heat source expansion valve 24is equal to or less than a predetermined opening. The opening of theheat source expansion valve 24 when the level of the refrigerant insidethe heat source heat exchanger 23 drops and it becomes difficult for therefrigerating machine oil to be discharged together with the evaporatedrefrigerant is found experimentally, and the predetermined opening isdetermined on the basis of the experimentally found opening.

<Cooling Operating Mode>

When all of the utilization units 3, 4 and 5 conduct the coolingoperation, the refrigerant circuit 12 of the air conditioner 1 isconfigured as shown in FIG. 5 (refer to the arrows added to therefrigerant circuit 12 in FIG. 5 for the flow of the refrigerant).Specifically, in the heat source refrigerant circuit 12 d of the heatsource unit 2, the first switch mechanism 22 is switched to thecondensation operating state (the state indicated by the solid lines ofthe first switch mechanism 22 in FIG. 5), whereby the heat source heatexchanger 23 is caused to function as a condenser. Further, the heatsource expansion valve 24 is opened. It will be noted that the controlvalve 101 b of the first oil returning circuit 101 is closed so that theoperation of extracting, and returning to the compression mechanism 21,the refrigerating machine oil together with the refrigerant from thelower portion of the heat source heat exchanger 23 is not conducted. Inthe connection units 6, 7 and 8, the high-pressure gas control valves66, 76 and 86 are closed and the low-pressure gas control valves 67, 77and 87 are opened, whereby the utilization heat exchangers 32, 42 and 52of the utilization units 3, 4 and 5 are caused to function asevaporators, and the utilization heat exchangers 32, 42 and 52 of theutilization units 3, 4 and 5 and the intake side of the compressionmechanism 21 of the heat source unit 2 become connected via thelow-pressure gas refrigerant communication pipe 11. In the utilizationunits 3, 4 and 5, the openings of the utilization expansion valves 31,41 and 51 are regulated in accordance with the cooling load of eachutilization unit, such as the openings being regulated on the basis ofthe degree of superheat of the utilization heat exchangers 32, 42 and 52(specifically, the temperature difference between the refrigeranttemperature detected by the liquid temperature sensors 33, 43 and 53 andthe refrigerant temperature detected by the gas temperature sensors 34,44 and 54), for example.

In this configuration of the refrigerant circuit 12, a large portion ofthe refrigerating machine oil accompanying the high-pressure gasrefrigerant that has been compressed and discharged by the compressor 21a of the compression mechanism 21 is separated in the oil separator 21b, and the high-pressure gas refrigerant is sent to the first switchmechanism 22. Then, the refrigerating machine oil separated in the oilseparator 21 b is returned to the intake side of the compressor 21 athrough the second oil returning circuit 21 d. The high-pressure gasrefrigerant sent to the first switch mechanism 22 is sent to the heatsource heat exchanger 23 through the first port 22 a and the second port22 b of the first switch mechanism 22. Then, the high-pressure gasrefrigerant sent to the heat source heat exchanger 23 is condensed inthe heat source heat exchanger 23 as a result of heat exchange beingconducted with water serving as a heat source. Then, the refrigerantcondensed in the heat source heat exchanger 23 passes through the heatsource expansion valve 24, the high-pressure gas refrigerant that hasbeen compressed and discharged by the compression mechanism 21 mergestherewith through the pressurizing circuit 111 (the details will bedescribed later), and the refrigerant is sent to the receiver 25. Then,the refrigerant sent to the receiver 25 is temporarily accumulatedinside the receiver 25 and thereafter sent to the cooler 121. Then, therefrigerant sent to the cooler 121 is cooled as a result of heatexchange being conducted with the refrigerant flowing through thecooling circuit 122 (the details will be described later). Then, therefrigerant cooled in the cooler 121 is sent to the liquid refrigerantcommunication pipe 9 through the liquid closing valve 27.

Then, the refrigerant sent to the liquid refrigerant communication pipe9 is branched into three and sent to the liquid connection pipes 61, 71and 81 of the connection units 6, 7 and 8. Then, the refrigerant sent tothe liquid connection pipes 61, 71 and 81 of the connection units 6, 7and 8 is sent to the utilization expansion valves 31, 41 and 51 of theutilization units 3, 4 and 5.

Then, the pressure of the refrigerant sent to the utilization expansionvalves 31, 41 and 51 is reduced by the utilization expansion valves 31,41 and 51, and the refrigerant is thereafter evaporated in theutilization heat exchangers 32, 42 and 52 as a result of heat exchangebeing conducted with the indoor air and becomes low-pressure gasrefrigerant. The indoor air is cooled and supplied to the indoors. Then,the low-pressure gas refrigerant is sent to the junction gas connectionpipes 65, 75 and 85 of the connection units 6, 7 and 8.

Then, the low-pressure gas refrigerant sent to the junction gasconnection pipes 65, 75 and 85 is sent to the low-pressure gasrefrigerant communication pipe 11 through the low-pressure gas controlvalves 67, 77 and 87 and the low-pressure gas connection pipes 64, 74and 84, and merges.

Then, the low-pressure gas refrigerant that has been sent to thelow-pressure gas refrigerant communication pipe 11 and merged isreturned to the intake side of the compression mechanism 21 through thelow-pressure gas closing valve 29. In this manner, the operation in thecooling operating mode is conducted.

At this time, there are cases where the cooling loads of the utilizationunits 3, 4 and 5 become extremely small. In such cases, it is necessaryto reduce the refrigerant condensing ability in the heat source heatexchanger 23 of the heat source unit 2 and balance the overall coolingload of the utilization units 3, 4 and 5 (specifically, the evaporationloads of the utilization heat exchangers 32, 42 and 52). For thisreason, control is conducted to reduce the condensation amount of therefrigerant in the heat source heat exchanger 23 by conducting controlto reduce the opening of the heat source expansion valve 24. Whencontrol is conducted to reduce the opening of the heat source expansionvalve 24, the amount of the liquid refrigerant accumulating inside theheat source heat exchanger 23 increases and the substantial heattransfer area is reduced, whereby the condensing ability becomessmaller. However, when control is conducted to reduce the opening of theheat source expansion valve 24, there is a tendency for the refrigerantpressure downstream of the heat source expansion valve 24 (specifically,between the heat source expansion valve 24 and the utilizationrefrigerant circuits 12 a, 12 b and 12 c) to drop and become unstable,and there is a tendency for it to become difficult to stably conductcontrol to reduce the condensing ability of the heat source refrigerantcircuit 12 d.

However, in the air conditioner 1 of the present embodiment, thepressurizing circuit 111 is disposed which causes the high-pressure gasrefrigerant compressed and discharged by the compression mechanism 21 tomerge with the refrigerant whose pressure is reduced in the heat sourceexpansion valve 24 and which is sent to the utilization refrigerantcircuits 12 a, 12 b and 12 c. Additionally, the control valve 111 b ofthe pressurizing circuit 111 is configured to be opened during thecooling operating mode (i.e., when the first switch mechanism 22 is inthe condensation operating state) such that it can cause the refrigerantto merge downstream of the heat source expansion valve 24 from thedischarge side of the compression mechanism 21 through the pressurizingpipe 111 a. For this reason, the pressure of the refrigerant downstreamof the heat source expansion valve 24 can be raised by causing thehigh-pressure gas refrigerant to merge through the pressurizing circuit111 downstream of the heat source expansion valve 24 while control isconducted to reduce the opening of the heat source expansion valve 24.However, when the high-pressure gas refrigerant is simply caused tomerge downstream of the heat source expansion valve 24 through thepressurizing circuit 111, the high-pressure gas refrigerant merges andthe refrigerant sent to the utilization refrigerant circuits 12 a, 12 band 12 c becomes a gas-liquid two-phase flow with a large gas fraction,and when the refrigerant is branched from the liquid refrigerantcommunication pipe 9 to the utilization refrigerant circuits 12 a, 12 band 12 c, drift arises between the utilization refrigerant circuits 12a, 12 b and 12 c.

However, in the air conditioner 1 of the present embodiment, the cooler121 is further disposed downstream of the heat source expansion valve24. For this reason, control is conducted to raise the refrigerantpressure downstream of the heat source expansion valve 24 by causing thehigh-pressure gas refrigerant to merge through the pressurizing circuit111 downstream of the heat source expansion valve 24 while control isconducted to reduce the opening of the heat source expansion valve 24,and the refrigerant whose pressure is reduced by the heat sourceexpansion valve 24 and which is sent to the utilization refrigerantcircuits 12 a, 12 b and 12 c is cooled by the cooler 121. For thisreason, the gas refrigerant can be condensed, and refrigerant of agas-liquid two-phase flow with a large gas fraction does not have to besent to the utilization refrigerant circuits 12 a, 12 b and 12 c.Further, in the air conditioner 1 of the present embodiment, because thepressurizing pipe 111 a is connected between the heat source expansionvalve 24 and the receiver 25, the high-pressure gas refrigerant mergeswith the refrigerant downstream of the heat source expansion valve 24,and the refrigerant whose temperature has risen as a result of thehigh-pressure gas refrigerant merging therewith is cooled by the cooler121. For this reason, it is not necessary to use a low-temperaturecooling source as the cooling source for cooling the refrigerant in thecooler 121, and a cooling source with a relatively high temperature canbe used. Moreover, in the air conditioner 1 of the present embodiment,the cooling circuit 122 is disposed, the pressure of some of therefrigerant sent from the heat source heat exchanger 23 to theutilization refrigerant circuits 12 a, 12 b and 12 c is reduced to arefrigerant pressure that can return it to the intake side of thecompression mechanism 21, and this refrigerant is used as the coolingsource of the cooler 121. For this reason, a cooling source can beobtained which has a sufficiently lower temperature than the temperatureof the refrigerant whose pressure is reduced in the heat sourceexpansion valve 24 and which is sent to the utilization refrigerantcircuits 12 a, 12 b and 12 c. For this reason, the refrigerant whosepressure is reduced in the heat source expansion valve 24 and which issent to the utilization refrigerant circuits 12 a, 12 b and 12 c can becooled to a subcooled state. Additionally, the opening of the coolingcircuit expansion valve 122 b of the cooling circuit 122 is regulated inaccordance with the flow rate and temperature of the refrigerant sent tothe utilization refrigerant circuits 12 a, 12 b and 12 c from downstreamof the heat source expansion valve 24, such as regulating the opening onthe basis of the degree of superheat of the cooler 121 (calculated fromthe refrigerant temperature detected by the cooling circuit outlettemperature sensor 96 disposed in the lead-out pipe 122 c of the coolingcircuit 122).

<Simultaneous Cooling and Heating Operating Mode (Evaporation Load)>

The operation will be described during the simultaneous cooling andheating operating mode where, for example, the utilization unit 3 of theutilization units 3, 4 and 5 conducts the cooling operation and theutilization units 4 and 5 conduct the heating operation, when the heatsource heat exchanger 23 of the heat source unit 2 is caused to functionand operate as an evaporator (evaporation operating mode). In this case,the refrigerant circuit 12 of the air conditioner 1 is configured asshown in FIG. 6 (refer to the arrows added to the refrigerant circuit 12in FIG. 6 for the flow of the refrigerant). Specifically, in the heatsource refrigerant circuit 12 d of the heat source unit 2, similar tothe aforementioned heating operating mode, the first switch mechanism 22is switched to the evaporation operating state (the state indicated bythe dotted lines of the first switch mechanism 22 in FIG. 6) and thesecond switch mechanism 26 is switched to the heating load requirementoperating state (the state indicated by the dotted lines of the secondswitch mechanism 26 in FIG. 6), whereby the heat source heat exchanger23 is caused to function as an evaporator so that the high-pressure gasrefrigerant compressed and discharged in the compression mechanism 21can be supplied to the utilization units 4 and 5 through thehigh-pressure gas refrigerant communication pipe 10. Further, theopening of the heat source expansion valve 24 is regulated to reduce thepressure of the refrigerant. It will be noted that the control valve 111b of the pressurizing circuit 111 and the cooling circuit expansionvalve 122 b of the cooling circuit 122 are closed so that thehigh-pressure gas refrigerant is not caused to merge with therefrigerant flowing between the heat source expansion valve 24 and thereceiver 25 and the supply of the cooling source to the cooler 121 iscut off such that that the refrigerant flowing between the receiver 25and the utilization units 3, 4 and 5 is not cooled. In the connectionunit 6, the high-pressure gas control valve 66 is closed and thelow-pressure gas control valve 67 is opened, whereby the utilizationheat exchanger 32 of the utilization unit 3 is caused to function as anevaporator, and the utilization heat exchanger 32 of the utilizationunit 3 and the intake side of the compression mechanism 21 of the heatsource unit 2 become connected via the low-pressure gas refrigerantcommunication pipe 11. In the utilization unit 3, the opening of theutilization expansion valve 31 is regulated in accordance with thecooling load of the utilization unit, such as the opening beingregulated on the basis of the degree of superheat of the utilizationheat exchanger 32 (specifically, the temperature difference between therefrigerant temperature detected by the liquid temperature sensor 33 andthe refrigerant temperature detected by the gas temperature sensor 34),for example. In the connection units 7 and 8, the low-pressure gascontrol valves 77 and 87 are closed and the high-pressure gas controlvalves 76 and 86 are opened, whereby the utilization heat exchangers 42and 52 of the utilization units 4 and 5 are caused to function ascondensers. In the utilization units 4 and 5, the openings of theutilization expansion valves 41 and 51 are regulated in accordance withthe heating load of each utilization unit, such as the openings beingregulated on the basis of the degree of subcooling of the utilizationheat exchangers 42 and 52 (specifically, the temperature differencebetween the refrigerant temperature detected by the liquid temperaturesensors 43 and 53 and the refrigerant temperature detected by the gastemperature sensors 44 and 54), for example.

In this configuration of the refrigerant circuit 12, a large portion ofthe refrigerating machine oil accompanying the high-pressure gasrefrigerant that has been compressed and discharged by the compressor 21a of the compression mechanism 21 is separated in the oil separator 21b, and the high-pressure gas refrigerant is sent to the second switchmechanism 26. Then, the refrigerating machine oil separated in the oilseparator 21 b is returned to the intake side of the compressor 21 athrough the second oil returning circuit 21 d. The high-pressure gasrefrigerant sent to the second switch mechanism 26 is sent to thehigh-pressure gas refrigerant communication pipe 10 through the firstport 26 a and the fourth port 26 d of the second switch mechanism 26 andthe high-pressure gas closing valve 28.

Then, the high-pressure gas refrigerant sent to the high-pressure gasrefrigerant communication pipe 10 is branched into two and sent to thehigh-pressure gas connection pipes 73 and 83 of the connection units 7and 8. The high-pressure gas refrigerant sent to the high-pressure gasconnection pipes 73 and 83 of the connection units 7 and 8 is sent tothe utilization heat exchangers 42 and 52 of the utilization units 4 and5 through the high-pressure gas control valves 76 and 86 and thejunction gas connection pipes 75 and 85.

Then, the high-pressure gas refrigerant sent to the utilization heatexchangers 42 and 52 is condensed in the utilization heat exchangers 42and 52 of the utilization units 4 and 5 as a result of heat exchangebeing conducted with the indoor air. The indoor air is heated andsupplied to the indoors. The refrigerant condensed in the utilizationheat exchangers 42 and 52 passes through the utilization expansionvalves 41 and 51 and is thereafter sent to the liquid connection pipes71 and 81 of the connection units 7 and 8.

Then, the refrigerant sent to the liquid connection pipes 71 and 81 issent to the liquid refrigerant communication pipe 9 and merges.

Then, some of the refrigerant that has been sent to the liquidrefrigerant communication pipe 9 and merged is sent to the liquidconnection pipe 61 of the connection unit 6. Then, the refrigerant sentto the liquid connection pipe 61 of the utilization unit 6 is sent tothe utilization expansion valve 31 of the utilization unit 3.

Then, the pressure of the refrigerant sent to the utilization expansionvalve 31 is reduced by the utilization expansion valve 31, and therefrigerant is evaporated in the utilization heat exchanger 32 as aresult of heat exchange being conducted with the indoor air and becomeslow-pressure gas refrigerant. The indoor air is cooled and supplied tothe indoors. Then, the low-pressure gas refrigerant is sent to thejunction gas connection pipe 65 of the connection unit 6.

Then, the low-pressure gas refrigerant sent to the junction gasconnection pipe 65 is sent to the low-pressure gas refrigerantcommunication pipe 11 through the low-pressure gas control valve 67 andthe low-pressure gas connection pipe 64, and merges.

Then, the low-pressure gas refrigerant sent to the low-pressure gasrefrigerant communication pipe 11 is returned to the intake side of thecompression mechanism 21 through the low-pressure gas closing valve 29.

The remaining refrigerant excluding the refrigerant sent from the liquidrefrigerant communication pipe 9 to the connection unit 6 and theutilization unit 3 is sent to the receiver 25 through the liquid closingvalve 27 and the cooler 121 of the heat source unit 2. The refrigerantsent to the receiver 25 is temporarily accumulated inside the receiver25, and the pressure of the refrigerant is thereafter reduced by theheat source expansion valve 24. Then, the refrigerant whose pressure hasbeen reduced by the heat source expansion valve 24 is evaporated in theheat source heat exchanger 23 as a result of heat exchange beingconducted with water serving as a heat source, becomes low-pressure gasrefrigerant, and is sent to the first switch mechanism 22. Then, thelow-pressure gas refrigerant sent to the first switch mechanism 22 isreturned to the intake side of the compression mechanism 21 through thesecond port 22 b and the third port 22 c of the first switch mechanism22. In this manner, the operation in the simultaneous cooling andheating operating mode (evaporation load) is conducted.

At this time, there are cases where, in accordance with the overall airconditioning load of the utilization units 3, 4 and 5, an evaporationload is necessary as the heat source heat exchanger 23 but the sizethereof becomes extremely small. In such cases, similar to theaforementioned heating operating mode, it is necessary to reduce therefrigerant evaporating ability in the heat source heat exchanger 23 ofthe heat source unit 2 and balance the overall air conditioning load ofthe utilization units 3, 4 and 5. In particular, there are cases wherethe cooling load of the utilization unit 3 and the heating loads of theutilization units 4 and 5 become about the same in the simultaneouscooling and heating operating mode, and in such cases the evaporationload of the heat source heat exchanger 23 must be extremely reduced.

However, in the air conditioner 1 of the present embodiment, because thecombination of refrigerating machine oil and refrigerant that does notseparate into two layers in a temperature range of 30° C. or below (morepreferably, the minimum value of the evaporation temperature or less) isused (i.e., a combination of refrigerating machine oil and refrigerantthat does not separate into two layers in the heat source heat exchangerwhen the heat source heat exchanger functions as an evaporator), and thefirst oil returning circuit 101 is disposed, the accumulation ofrefrigerating machine oil inside the heat source heat exchanger 23 canbe prevented as previously mentioned in the description of the operationof the heating operating mode.

<Simultaneous Cooling and Heating Mode (Condensation Load)>

The operation will be described during the simultaneous cooling andheating operating mode where, for example, the utilization units 3 and 4of the utilization units 3, 4 and 5 conduct the cooling operation andthe utilization unit 5 conducts the heating operation, when the heatsource heat exchanger 23 of the heat source unit 2 is caused to functionand operate as a condenser in accordance with the overall airconditioning load of the utilization units 3, 4 and 5 (condensationoperating mode). In this case, the refrigerant circuit 12 of the airconditioner 1 is configured as shown in FIG. 7 (refer to the arrowsadded to the refrigerant circuit 12 in FIG. 7 for the flow of therefrigerant). Specifically, in the heat source refrigerant circuit 12 dof the heat source unit 2, the first switch mechanism 22 is switched tothe condensation operating state (the state indicated by the solid linesof the first switch mechanism 22 in FIG. 7) and the second switchmechanism 26 is switched to the heating load requirement operating state(the state indicated by the dotted lines of the second switch mechanism26 in FIG. 7), whereby the heat source heat exchanger 23 is caused tofunction as an evaporator so that the high-pressure gas refrigerantcompressed and discharged in the compression mechanism 21 can besupplied to the utilization unit 5 through the high-pressure gasrefrigerant communication pipe 10. Further, the heat source expansionvalve 24 is opened. It will be noted that the control valve 101 b of thefirst oil returning circuit 101 is closed so that the operation ofextracting, and returning to the compression mechanism 21, therefrigerating machine oil together with the refrigerant from the lowerportion of the heat source heat exchanger 23 is not conducted. In theconnection units 6 and 7, the high-pressure gas control valves 66 and 76are closed and the low-pressure gas control valves 67 and 77 are opened,whereby the utilization heat exchangers 32 and 42 of the utilizationunits 3 and 4 are caused to function as evaporators, and the utilizationheat exchangers 32 and 42 of the utilization units 3 and 4 and theintake side of the compression mechanism 21 of the heat source unit 2become connected via the low-pressure gas refrigerant communication pipe11. In the utilization units 3 and 4, the openings of the utilizationexpansion valves 31 and 41 are regulated in accordance with the coolingload of each utilization unit, such as the openings being regulated onthe basis of the degree of superheat of the utilization heat exchangers32 and 42 (specifically, the temperature difference between therefrigerant temperature detected by the liquid temperature sensors 33and 43 and the refrigerant temperature detected by the gas temperaturesensors 34 and 44), for example. In the connection unit 8, thelow-pressure gas control valve 87 is closed and the high-pressure gascontrol valve 86 is opened, whereby the utilization heat exchanger 52 ofthe utilization unit 5 is caused to function as a condenser. In theutilization unit 5, the opening of the utilization expansion valve 51 isregulated in accordance with the heating load of the utilization unit,such as the opening being regulated on the basis of the degree ofsubcooling of the utilization heat exchanger 52 (specifically, thetemperature difference between the refrigerant temperature detected bythe liquid temperature sensor 53 and the refrigerant temperaturedetected by the gas temperature sensor 54), for example.

In this configuration of the refrigerant circuit 12, a large portion ofthe refrigerating machine oil accompanying the high-pressure gasrefrigerant that has been compressed and discharged by the compressor 21a of the compression mechanism 21 is separated in the oil separator 21b, and the high-pressure gas refrigerant is sent to the first switchmechanism 22 and the second switch mechanism 26. Then, the refrigeratingmachine oil separated in the oil separator 21 b is returned to theintake side of the compressor 21 a through the second oil returningcircuit 21 d. Then, the high-pressure gas refrigerant sent to the firstswitch mechanism 22 of the high-pressure gas refrigerant that has beencompressed and discharged by the compression mechanism 21 is sent to theheat source heat exchanger 23 through the first port 22 a and the secondport 22 b of the first switch mechanism 22. Then, the high-pressure gasrefrigerant sent to the heat source heat exchanger 23 is condensed inthe heat source heat exchanger 23 as a result of heat exchange beingconducted with water serving as a heat source. Then, the refrigerantcondensed in the heat source heat exchanger 23 passes through the heatsource expansion valve 24, the high-pressure gas refrigerant that hasbeen compressed and discharged by the compression mechanism 21 mergestherewith through the pressurizing circuit 111 (the details will bedescribed later), and the refrigerant is sent to the receiver 25. Then,the refrigerant sent to the receiver 25 is temporarily accumulatedinside the receiver 25 and sent to the cooler 121. Then, the refrigerantsent to the cooler 121 is cooled as a result of heat exchange beingconducted with the refrigerant flowing through the cooling circuit 122(the details will be described later). Then, the refrigerant cooled inthe cooler 121 is sent to the liquid refrigerant communication pipe 9through the liquid closing valve 27.

The high-pressure gas refrigerant sent to the second switch mechanism 26of the high-pressure gas refrigerant that has been compressed anddischarged by the compression mechanism 21 is sent to the high-pressuregas refrigerant communication pipe 10 through the first port 26 a andthe second port 26 d of the second switch mechanism 26 and thehigh-pressure gas closing valve 28.

Then, the high-pressure gas refrigerant sent to the high-pressure gasrefrigerant communication pipe 10 is sent to the high-pressure gasconnection pipe 83 of the connection unit 8. The high-pressure gasrefrigerant sent to the high-pressure gas connection pipe 83 of theconnection unit 8 is sent to the utilization heat exchanger 52 of theutilization unit 5 through the high-pressure gas control valve 86 andthe junction gas connection pipe 85.

Then, the high-pressure gas refrigerant sent to the utilization heatexchanger 52 is condensed in the utilization heat exchanger 52 of theutilization unit 5 as a result of heat exchange being conducted with theindoor air. The indoor air is heated and supplied to the indoors. Therefrigerant condensed in the utilization heat exchanger 52 passesthrough the utilization expansion valve 51 and is thereafter sent to theliquid connection pipe 81 of the connection unit 8.

Then, the refrigerant sent to the liquid connection pipe 81 is sent tothe liquid refrigerant communication pipe 9 and merges with therefrigerant sent to the liquid refrigerant communication pipe 9 throughthe first switch mechanism 22, the heat source heat exchanger 23, theheat source expansion valve 24, the receiver 25, the cooler 121 and theliquid closing valve 27.

Then, the refrigerant flowing through the liquid refrigerantcommunication pipe 9 is branched into two and sent to the liquidconnection pipes 61 and 71 of the connection units 6 and 7. Then, therefrigerant sent to the liquid connection pipes 61 and 71 of theconnection units 6 and 7 is sent to the utilization expansion valves 31and 41 of the utilization units 3 and 4.

Then, the pressure of refrigerant sent to the utilization expansionvalves 31 and 41 is reduced by the utilization expansion valves 31 and41, and the refrigerant is thereafter evaporated in the utilization heatexchangers 32 and 42 as a result of heat exchange being conducted withthe indoor air and becomes low-pressure gas refrigerant. The indoor airis cooled and supplied to the indoors. Then, the low-pressure gasrefrigerant is sent to the junction gas connection pipes 65 and 75 ofthe connection units 6 and 7.

Then, the low-pressure gas refrigerant sent to the junction gasconnection pipes 65 and 75 is sent to the low-pressure gas refrigerantcommunication pipe 11 through the low-pressure gas control valves 67 and77 and the low-pressure gas connection pipes 64 and 74, and merges.

Then, the low-pressure gas refrigerant sent to the low-pressure gasrefrigerant communication pipe 11 is returned to the intake side of thecompression mechanism 21 through the low-pressure gas closing valve 29.In this manner, the operation in the simultaneous cooling and heatingoperating mode (condensation load) is conducted.

At this time, there are cases where, in accordance with the overall airconditioning load of the utilization units 3, 4 and 5, a condensationload is necessary for the heat source heat exchanger 23 but the sizethereof becomes extremely small. In such cases, similar to theaforementioned cooling operating mode, it is necessary to reduce therefrigerant condensing ability in the heat source heat exchanger 23 ofthe heat source unit 2 and balance the overall air conditioning load ofthe utilization units 3, 4 and 5. In particular, there are cases wherethe cooling loads of the utilization units 3 and 4 and the heating loadof the utilization unit 5 become about the same in the simultaneouscooling and heating operating mode, and in such cases the condensationload of the heat source heat exchanger 23 must be made extremely small.

However, in the air conditioner 1 of the present embodiment, control isconducted to raise the pressure of the refrigerant downstream of theheat source expansion valve 24 by causing the high-pressure gasrefrigerant to merge through the pressurizing circuit 111 downstream ofthe heat source expansion valve 24 while reducing the opening of theheat source expansion valve 24, and the refrigerant whose pressure isreduced by the heat source expansion valve 24 and which is sent to theutilization refrigerant circuits 12 a and 12 b is cooled by the cooler121. For this reason, the gas refrigerant can be condensed, andrefrigerant of a gas-liquid two-phase flow with a large gas fractiondoes not have to be sent to the utilization refrigerant circuits 12 aand 12 b.

(3) Characteristics of the Air Conditioner

The air conditioner 1 of the present embodiment has the followingcharacteristics.

(A)

The air conditioner 1 of the present embodiment is provided with therefrigerant circuit 12 configured by the interconnection of theplurality of utilization refrigerant circuits 12 a, 12 b and 12 c andthe heat source refrigerant circuit 12 d, which includes the heat sourceheat exchanger 23 configured such that the refrigerant flows in frombelow and flows out from above when the heat source heat exchanger 23functions as an evaporator. A combination of refrigerating machine oiland refrigerant that does not separate into two layers in a temperaturerange of 30° C. or below (more preferably, the minimum value of theevaporation temperature or less) is used as the refrigerating machineoil and the refrigerant used in the refrigerant circuit 12. Here, theevaporation temperature of the refrigerant in the heat source heatexchanger 23 is a temperature of 30° C. or below (more preferably, theminimum value of the evaporation temperature or less) when water, air,and brine are used as the heat sources. Specifically, a combination ofrefrigerating machine oil and refrigerant that does not separate intotwo layers in the heat source heat exchanger is used as therefrigerating machine oil and refrigerant in the refrigerant circuitwhen the heat source heat exchanger functions as an evaporator. For thisreason, in the air conditioner 1, the refrigerating machine oil does notaccumulate in a state where it floats on the surface of the refrigerantinside the heat source heat exchanger 23, but rather accumulates insidethe heat source heat exchanger 23 in a state where it is mixed with therefrigerant. Additionally, the refrigerating machine oil accumulatinginside the heat source heat exchanger 23 is returned to the intake sideof the compression mechanism 21 together with the refrigerant by thefirst oil returning circuit 101 connected to the lower portion of theheat source heat exchanger 23. For this reason, it becomes unnecessaryto maintain the level of the refrigerant inside the heat source heatexchanger at a constant level or more in order to prevent therefrigerating machine oil from accumulating inside the heat source heatexchanger, as in conventional air conditioners.

Thus, in the air conditioner 1, even when control is conducted to reducethe evaporating ability of the heat source heat exchanger 23 by reducingthe opening of the heat source expansion valve 24 in accordance with theair conditioning load of the plurality of utilization refrigerantcircuits 12 a, 12 b and 12 c so that as a result the level of therefrigerant inside the heat source heat exchanger 23 drops, therefrigerating machine oil does not accumulate inside the heat sourceheat exchanger 23. For this reason, the control width when theevaporating ability of the heat source heat exchanger 23 is controlledwith a heat source expansion valve can be expanded.

Additionally, in the air conditioner 1, it becomes unnecessary toconduct control, as in conventional air conditioners disposed withplural heat source heat exchangers, to reduce the evaporating ability byclosing some of the heat source expansion valves to reduce the number ofheat source heat exchangers functioning as evaporators when the heatsource heat exchangers are caused to function as evaporators or toreduce the evaporating ability by causing some of the heat source heatexchangers to function as condensers to offset the evaporating abilityof the heat source heat exchangers functioning as evaporators. For thisreason, a wide control width of the evaporating ability can be obtainedby a single heat source heat exchanger.

Thus, because simplification of the heat source heat exchanger becomespossible in an air conditioner where simplification of the heat sourceheat exchangers could not be realized by restricting the control widthof the control of the evaporating ability of the heat source heatexchangers, increases in the number of parts and cost that had occurredin conventional air conditioners as a result of disposing plural heatsource heat exchangers can be prevented. Further, the problem of the COPbecoming poor can be eliminated in an operating condition where, whensome of the heat source heat exchangers are caused to function ascondensers to reduce the evaporating ability, the amount of refrigerantcompressed in the compression mechanism increases in correspondence tothe amount of refrigerant condensed by the heat source heat exchangers,and the air conditioning load of the entire plurality of utilizationrefrigerant circuits is small.

(B)

In the air conditioner 1 of the present embodiment, the control valve101 b is disposed in the first oil returning circuit 101, and the airconditioner 1 operates in a state where the control valve 101 b isclosed when the heat source heat exchanger 23 is caused to function as acondenser, whereby the amount of refrigerant sent to the utilizationrefrigerant circuits 12 a, 12 b and 12 c after being condensed in theheat source heat exchanger 23 can be prevented from being reduced.

Further, in the air conditioner 1, it is not necessary to use the firstoil returning circuit 101 until the level of the refrigerant inside theheat source heat exchanger 23 reaches a constant level or more wherethere is no accumulation of refrigerating machine oil. For this reason,the opening of the heat source expansion valve 24 corresponding to alevel of the refrigerant where accumulation of the refrigerating machineoil can occur inside the heat source heat exchanger 23 is set as apredetermined opening, and the control valve 101 b is opened and the airconditioner 1 operates only when the opening of the heat sourceexpansion valve 24 becomes equal to or less than this predeterminedopening, whereby the amount of refrigerant sent to the compressionmechanism 21 can be prevented from increasing without the refrigerantbeing evaporated in the heat source heat exchanger 23.

(C)

In the air conditioner 1 of the present embodiment, a plate-type heatexchanger is used as the heat source heat exchanger 23, and in terms ofthe structure thereof, it is difficult for the refrigerating machine oilaccumulating in a state where it floats on the surface of therefrigerant to be extracted from the vicinity of the surface of therefrigerant in order to prevent the refrigerating machine oil fromaccumulating inside the heat source heat exchanger 23. However, in theair conditioner 1 of the present embodiment, it suffices simply for therefrigerating machine oil to accumulate inside the heat source heatexchanger 23 in a state where it is mixed with the refrigerant and forthe refrigerating machine oil accumulating inside the heat sourceexchanger 23 to be extracted from the lower portion of the heat sourceheat exchanger 23 together with the refrigerant. For this reason, it iseasy to dispose the first oil returning circuit 101 even when aplate-type heat exchanger is used.

(D)

In the air conditioner 1 of the present embodiment, the high-pressuregas refrigerant merges from the pressurizing circuit 111 and therefrigerant to be sent to the utilization refrigerant circuits 12 a, 12b and 12 c is pressurized so that the refrigerant pressure downstream ofthe heat source expansion valve 24 rises when the pressure of therefrigerant that has been condensed in the heat source heat exchanger 23functioning as a condenser is reduced by the heat source expansion valve24 and the refrigerant is sent to the utilization refrigerant circuits12 a, 12 b and 12 c. Here, when the high-pressure gas refrigerant issimply caused to merge as in conventional air conditioners, therefrigerant sent to the utilization refrigerant circuits 12 a, 12 b and12 c becomes a gas-liquid two-phase flow with a large gas fraction sothat as a result the opening of the heat source expansion valve 24cannot be sufficiently reduced. However, in the air conditioner 1, therefrigerant whose pressure is reduced by the heat source expansion valve24 and which is sent to the utilization refrigerant circuits 12 a, 12 band 12 c is cooled by the cooler 121. For this reason, the gasrefrigerant can be condensed, and refrigerant of a gas-liquid two-phaseflow with a large gas fraction does not have to be sent to theutilization refrigerant circuits 12 a, 12 b and 12 c.

Thus, in the air conditioner 1, even if control is conducted to reducethe condensing ability of the heat source heat exchanger 23 by reducingthe opening of the heat source expansion valve 24 in accordance with theair conditioning load of the plurality of utilization refrigerantcircuits 12 a, 12 b and 12 c and control is conducted with thepressurizing circuit 111 to merge the high-pressure gas refrigerant andpressurize the refrigerant sent to the utilization refrigerant circuits12 a, 12 b and 12 c, refrigerant of a gas-liquid two-phase flow with alarge gas fraction does not have to be sent to the utilizationrefrigerant circuits 12 a, 12 b and 12 c. For this reason, the controlwidth when the evaporating ability of the heat source heat exchanger 23is controlled by the heat source expansion valve 24 can be expanded.

Additionally, in the air conditioner 1, it becomes unnecessary toconduct control, as in conventional air conditioners disposed withplural heat source heat exchangers, to reduce the evaporating ability byclosing some of the heat source expansion valves to reduce the number ofheat source heat exchangers functioning as evaporators when the heatsource heat exchangers are caused to function as condensers or to reducethe evaporating ability by causing some of the heat source heatexchangers to function as condensers to offset the evaporating abilityof the heat source heat exchangers functioning as evaporators. For thisreason, a wide control width of the condensing ability can be obtainedby a single heat source heat exchanger.

Thus, because simplification of the heat source heat exchanger becomespossible in an air conditioner where simplification of the heat sourceheat exchangers could not be realized by restricting the control widthof the control of the condensing ability of the heat source heatexchangers, increases in the number of parts and cost that had occurredin conventional air conditioners as a result of disposing plural heatsource heat exchangers can be prevented. Further, the problem of the COPbecoming poor can be eliminated in an operating condition where, whensome of the heat source heat exchangers are caused to function asevaporators to reduce the condensing ability, the amount of refrigerantcompressed in the compression mechanism increases in correspondence tothe amount of refrigerant condensed by the heat source heat exchangers,and the air conditioning load of the entire plurality of utilizationrefrigerant circuits is small.

(E)

In the air conditioner 1 of the present embodiment, because thepressurizing circuit 111 is connected between the heat source expansionvalve 24 and the cooler 121 such that the high-pressure gas refrigerantmerges, refrigerant whose temperature has become higher as a result ofthe high-pressure gas refrigerant merging therewith becomes cooled bythe cooler 121. Thus, it is not necessary to use a low-temperaturecooling source as the cooling source for cooling the refrigerant in thecooler 121, and a cooling source with a relatively high temperature canbe used.

Further, in the air conditioner 1, because refrigerant whose pressure isreduced to a refrigerant pressure that can return, to the intake side ofthe compression mechanism 21, some of the refrigerant sent fromdownstream of the heat source expansion valve 24 to the utilizationrefrigerant circuits 12 a, 12 b and 12 c is used as the cooling sourceof the cooler 121, a cooling source with a sufficiently lowertemperature than the temperature of the refrigerant sent from downstreamof the heat source expansion valve 24 to the utilization refrigerantcircuits 12 a, 12 b and 12 c can be obtained. Thus, the refrigerant sentfrom downstream of the heat source expansion valve 24 to the utilizationrefrigerant circuits 12 a, 12 b and 12 c can be cooled to a subcooledstate.

(F)

In the air conditioner 1 of the present embodiment, water, of which aconstant amount is supplied without relation to the control of the flowrate of the refrigerant flowing through the heat source heat exchanger23, is used, and the evaporating ability in the heat source heatexchanger 23 cannot be controlled by controlling the water amount.However, in the air conditioner 1, because the control width when theevaporating ability or the condensing ability of the heat source heatexchanger 23 is controlled by the heat source expansion valve 24 isexpanded, the control width when controlling the evaporating ability ofthe heat source heat exchanger 23 can be ensured even if the wateramount is not controlled.

(4) Modification 1

In the aforementioned air conditioner 1, the heat source unit 2 and theutilization units 3, 4 and 5 are connected via the refrigerantcommunication pipes 9, 10 and 11 and the connection units 6, 7 and 8 inorder to configure an air conditioner capable of simultaneous coolingand heating. However, as shown in FIG. 8, the heat source unit 2 and theutilization units 3, 4 and 5 may also be connected via only therefrigerant communication pipes 9 and 10 in order to configure an airconditioner capable of simultaneous cooling and heating. Specifically,the air conditioner 1 of the present modification is configured suchthat the low-pressure gas refrigerant communication pipe 11 and theconnection units 6, 7 and 8 necessary for making the air conditionercapable of simultaneous cooling and heating are omitted, the utilizationunits 3, 4 and 5 are directly connected to the liquid refrigerantcommunication pipe 9 and the high-pressure gas refrigerant communicationpipe 10, and by the switching of the second switch mechanism 26, thehigh-pressure gas refrigerant communication pipe 10 is caused tofunction as a pipe through which flows the low-pressure gas refrigerantreturned to the heat source unit 2 from the utilization units 3, 4 and5, and the high-pressure gas refrigerant communication pipe 10 is causedto function as a pipe through which flows the high-pressure gasrefrigerant supplied to the utilization units 3, 4 and 5 from the heatsource unit 2.

Next, the operation (the heating operating mode and the coolingoperating mode) of the air conditioner 1 of the present modificationwill be described.

First, the heating operating mode will be described. When all of theutilization units 3, 4 and 5 conduct the heating operation, therefrigerant circuit 12 of the air conditioner 1 is configured as shownin FIG. 9 (refer to the arrows added to the refrigerant circuit 12 inFIG. 9 for the flow of the refrigerant). Specifically, in the heatsource refrigerant circuit 12 d of the heat source unit 2, the firstswitch mechanism 22 is switched to the evaporation operating state (thestate indicated by the dotted lines of the first switch mechanism 22 inFIG. 9) and the second switch mechanism 26 is switched to the heatingload requirement operating state (the state indicated by the dottedlines of the second switch mechanism 26 in FIG. 9), whereby the heatsource heat exchanger 23 is caused to function as an evaporator so thatthe high-pressure gas refrigerant that has been compressed in thecompression mechanism 21 and discharged can be supplied to theutilization units 3, 4 and 5 through the high-pressure gas refrigerantcommunication pipe 10. Further, the opening of the heat source expansionvalve 24 is regulated to reduce the pressure of the refrigerant. It willbe noted that the control valve 111 b of the pressurizing circuit 111and the cooling circuit expansion valve 122 b of the cooling circuit 122are closed such that the high-pressure gas refrigerant is not caused tomerge with the refrigerant flowing between the heat source expansionvalve 24 and the receiver 25 and the supply of the cooling source to thecooler 121 is cut off so that the refrigerant flowing between thereceiver 25 and the utilization units 3, 4 and 5 is not cooled. In theutilization units 3, 4 and 5, the openings of the utilization expansionvalves 31, 41 and 51 are regulated in accordance with the heating loadof each utilization unit, such as the openings being regulated on thebasis of the degree of subcooling of the utilization heat exchangers 32,42 and 52 (specifically, the temperature difference between therefrigerant temperature detected by the liquid temperature sensors 33,43 and 53 and the refrigerant temperature detected by the gastemperature sensors 34, 44 and 54), for example.

In this configuration of the refrigerant circuit 12, a large portion ofthe refrigerating machine oil accompanying the high-pressure gasrefrigerant that has been compressed and discharged by the compressor 21a of the compression mechanism 21 is separated in the oil separator 21b, and the high-pressure gas refrigerant is sent to the second switchmechanism 26. Then, the refrigerating machine oil separated in the oilseparator 21 b is returned to the intake side of the compressor 21 athrough the second oil returning circuit 21 d. The high-pressure gasrefrigerant sent to the second switch mechanism 26 is sent to thehigh-pressure gas refrigerant communication pipe 10 through the firstport 26 a and the fourth port 26 d of the second switch mechanism 26 andthe high-pressure gas closing valve 28.

Then, the high-pressure gas refrigerant sent to the high-pressure gasrefrigerant communication pipe 10 is branched into three and sent to theutilization heat exchangers 32, 42 and 52 of the utilization units 3, 4and 5.

Then, the high-pressure gas refrigerant sent to the utilization heatexchangers 32, 42 and 52 is condensed in the utilization heat exchangers32, 42 and 52 of the utilization units 3, 4 and 5 as a result of heatexchange being conducted with the indoor air. The indoor air is heatedand supplied to the indoors. The refrigerant condensed in theutilization heat exchangers 32, 42 and 52 passes through the utilizationexpansion valves 31, 41 and 51, is thereafter sent to the liquidrefrigerant communication pipe 9, and merges.

Then, the refrigerant that has been sent to the liquid refrigerantcommunication pipe 9 and merged is sent to the receiver 25 through theliquid closing valve 27 and the cooler 121 of the heat source unit 2.The refrigerant sent to the receiver 25 is temporarily accumulatedinside the receiver 25, and the pressure of the refrigerant isthereafter reduced by the heat source expansion valve 24. Then, therefrigerant whose pressure has been reduced by the heat source expansionvalve 24 is evaporated in the heat source heat exchanger 23 as a resultof heat exchange being conducted with water serving as a heat source,becomes low-pressure gas refrigerant, and is sent to the first switchmechanism 22. Then, the low-pressure gas refrigerant sent to the firstswitch mechanism 22 is returned to the intake side of the compressionmechanism 21 through the second port 22 b and the third port 22 c of thefirst switch mechanism 22. In this manner, the operation in the heatingoperating mode is conducted.

In this case also, there are cases where the heating loads of theutilization units 3, 4 and 5 become extremely small, but because thecombination of refrigerating machine oil and refrigerant that does notseparate into two layers in a temperature range of 30° C. or below (morepreferably, the minimum value of the evaporation temperature or less) isused (i.e., a combination of refrigerating machine oil and refrigerantthat does not separate into two layers in the heat source heat exchangerwhen the heat source heat exchanger functions as an evaporator), and theoil returning circuit 101 is disposed, accumulation of the refrigeratingmachine oil inside the heat source heat exchanger 23 can be prevented inthe same manner as in the aforementioned heating operating mode of theair conditioner configured to be capable of simultaneous cooling andheating.

Next, the cooling operating mode will be described. When all of theutilization units 3, 4 and 5 conduct the cooling operation, therefrigerant circuit 12 of the air conditioner 1 is configured as shownin FIG. 10 (refer to the arrows added to the refrigerant circuit 12 inFIG. 10 for the flow of the refrigerant). Specifically, in the heatsource refrigerant circuit 12 d of the heat source unit 2, the firstswitch mechanism 22 is switched to the condensation operating state (thestate indicated by the solid lines of the first switch mechanism 22 inFIG. 10) and the second switch mechanism 26 is switched to thecooling/heating switching time cooling operating state (the stateindicated by the solid lines of the second switch mechanism 26 in FIG.10), whereby the heat source heat exchanger 23 is caused to function asa condenser so that the low-pressure gas refrigerant returned to theheat source unit 2 from the utilization units 3, 4 and 5 through thehigh-pressure gas refrigerant communication pipe 10 can be sent to theintake side of the compression mechanism 21. Further, the heat sourceexpansion valve 24 is opened. It will be noted that the control valve101 b of the first oil returning circuit 101 is closed so that theoperation of extracting, and returning to the compression mechanism 21,the refrigerating machine oil together with the refrigerant from thelower portion of the heat source heat exchanger 23 is not conducted. Inthe utilization units 3, 4 and 5, the openings of the utilizationexpansion valves 31, 41 and 51 are regulated in accordance with thecooling load of each utilization unit, such as the openings beingregulated on the basis of the degree of superheat of the utilizationheat exchangers 32, 42 and 52 (specifically, the temperature differencebetween the refrigerant temperature detected by the liquid temperaturesensors 33, 43 and 53 and the refrigerant temperature detected by thegas temperature sensors 34, 44 and 54), for example.

In this configuration of the refrigerant circuit 12, a large portion ofthe refrigerating machine oil accompanying the high-pressure gasrefrigerant that has been compressed and discharged by the compressor 21a of the compression mechanism 21 is separated in the oil separator 21b, and the high-pressure gas refrigerant is sent to the first switchmechanism 22. Then, the refrigerating machine oil separated in the oilseparator 21 b is returned to the intake side of the compressor 21 athrough the second oil returning circuit 21 d. Then, the high-pressuregas refrigerant sent to the first switch mechanism 22 is sent to theheat source heat exchanger 23 through the first port 22 a and the secondport 22 b of the first switch mechanism 22. Then, the high-pressure gasrefrigerant sent to the heat source heat exchanger 23 is condensed inthe heat source heat exchanger 23 as a result of heat exchange beingconducted with water serving as a heat source. Then, the refrigerantcondensed in the heat source heat exchanger 23 passes through the heatsource expansion valve 24, the high-pressure gas refrigerant that hasbeen compressed and discharged by the compression mechanism 21 throughthe pressurizing circuit 111 merges therewith, and the refrigerant issent to the receiver 25. Then, the refrigerant sent to the receiver 25is temporarily accumulated inside the receiver 25 and thereafter sent tothe cooler 121. Then, the refrigerant sent to the cooler 121 is cooledas a result of heat exchange being conducted with the refrigerantflowing through the cooling circuit 122. Then, the refrigerant cooled inthe cooler 121 is sent to the liquid refrigerant communication pipe 9through the liquid closing valve 27.

Then, the refrigerant sent to the liquid refrigerant communication pipe9 is branched into three and sent to the utilization expansion valves31, 41 and 51 of the utilization units 3, 4 and 5.

Then, the pressure of the refrigerant sent to the utilization expansionvalves 31, 41 and 51 is reduced by the utilization expansion valves 31,41 and 51, and the refrigerant is thereafter evaporated in theutilization heat exchangers 32, 42 and 52 as a result of heat exchangebeing conducted with the indoor air and becomes low-pressure gasrefrigerant. The indoor air is cooled and supplied to the indoors. Then,the low-pressure gas refrigerant is sent to the high-pressure gasrefrigerant communication pipe 10 and merges.

Then, the low-pressure gas refrigerant that has been sent to thehigh-pressure gas refrigerant communication pipe 10 and merged isreturned to the intake side of the compression mechanism 21 through thehigh-pressure gas closing valve 28 and the fourth port 26 d and thethird port 26 c of the second switch mechanism 26. In this manner, theoperation in the cooling operating mode is conducted.

In this case also, there are cases where the cooling loads of theutilization units 3, 4 and 5 become extremely small, but control isconducted to raise the pressure of the refrigerant downstream of theheat source expansion valve 24 by causing the high-pressure gasrefrigerant to merge through the pressurizing circuit 111 downstream ofthe heat source expansion valve 24 while conducting control to reducethe opening of the heat source expansion valve 24, and the refrigerantwhose pressure is reduced by the heat source expansion valve 24 andwhich is sent to the utilization refrigerant circuits 12 a, 12 b and 12c is cooled by the cooler 121. For this reason, in the same manner asthe aforementioned cooling operating mode of the air conditionerconfigured to be capable of simultaneous cooling and heating, the gasrefrigerant can be condensed, and refrigerant of a gas-liquid two-phaseflow with a large gas fraction does not have to be sent to theutilization refrigerant circuits 12 a, 12 b and 12 c.

(5) Modification 2

In the aforementioned air conditioner 1, the first oil returning circuit101, the pressurizing circuit 111, the cooler 121 and the coolingcircuit 122 were disposed in the heat source unit 2 in order to expandboth the control width of the control of the evaporating ability of theheat source heat exchanger 23 with the heat source expansion valve 24and the control width of the control of the condensing ability of theheat source heat exchanger 23 with the heat source expansion valve 24.However, when the control width of the control of the condensing abilityof the heat source heat exchanger 23 is ensured and it is necessary toexpand only the control width of the control of the evaporating abilityof the heat source heat exchanger 23, for example, just the first oilreturning circuit 101 (i.e., omitting the pressurizing circuit 111, thecooler 121 and the cooling circuit 122) may be disposed in the heatsource unit 2 as shown in FIG. 11 (i.e., the pressurizing circuit 111,the cooler 121 and the cooling circuit 122 may be omitted).

(6) Modification 3

In the aforementioned air conditioner 1, four-way switch valves wereused as the first switch mechanism 22 and the second switch mechanism26, but the switch mechanisms are not limited thereto. For example, asshown in FIG. 12, three-way switch valves may also be used as the firstswitch mechanism 22 and the second switch mechanism 26.

(7) Modification 4

In the aforementioned air conditioner 1, the flow rate of therefrigerating machine oil and the refrigerant returned to thecompression mechanism 21 from the lower portion of the heat source heatexchanger 23 functioning as an evaporator through the first oilreturning circuit 101 is determined in the first oil returning circuit101 in accordance with the pressure loss between the lower portion ofthe heat source heat exchanger 23 functioning as an evaporator and thecompression mechanism 21. For this reason, in cases where, for example,the pressure loss inside the heat source heat exchanger 23 functioningas an evaporator and inside the pipe from the refrigerant outlet side ofthe heat source heat exchanger 23 to the intake side of the compressionmechanism 21 is small and the pressure loss in the first oil returningcircuit 101 ends up becoming small, cases can arise where therefrigerating machine oil and the refrigerant of a flow rate sufficientenough to be able to prevent the refrigerating machine oil fromaccumulating inside the heat source heat exchanger 23 cannot be returnedto the compression mechanism 21 from the lower portion of the heatsource heat exchanger 23 through the first oil returning circuit 101.

In such cases, in order to ensure that the refrigerating machine oil andthe refrigerant of a flow rate sufficient enough to be able to preventthe refrigerating machine oil from accumulating inside the heat sourceheat exchanger 23 can be returned to the compression mechanism 21 fromthe lower portion of the heat source heat exchanger 23 through the firstoil returning circuit 101, as shown in FIG. 13, the air conditioner 1may be further disposed with a pressure reducing mechanism 131 that isconnected between the refrigerant outlet side of the heat source heatexchanger 23 and the intake side of the compression mechanism 21 and canreduce, before the refrigerating machine oil and the refrigerantreturned to the compression mechanism 21 from the lower portion of theheat source heat exchanger 23 through the first oil returning circuit101 merge, the pressure of the gas refrigerant evaporated in the heatsource heat exchanger 23 and returned to the intake side of thecompression mechanism.

The pressure reducing mechanism 131 mainly comprises a control valve 131a, which comprises an electromagnetic valve connected to the pipeconnecting the third port 22 c of the first switch mechanism 22 and theintake side of the compression mechanism 21, and a bypass pipe 131 b,which bypasses the control valve 131 a. A capillary tube 131 c isconnected to the bypass pipe 131 b. The pressure reducing mechanism 131can be operated such that when the first oil returning circuit 101 isused, the control valve 131 a is closed so that the gas refrigerantevaporated in the heat source heat exchanger 23 flows just through thebypass pipe 131 b, and in other cases, the control valve 131 a is openedso that the gas refrigerant evaporated in the heat source heat exchanger23 flows through both the control valve 131 a and the bypass pipe 131 b.For this reason, when the first oil returning circuit 101 is used, thepressure loss from the refrigerant outlet side of the heat source heatexchanger 23 functioning as an evaporator to the intake side of thecompression mechanism is increased (i.e., by causing the pressurereducing mechanism 131 to function as a pressure difference increasingmechanism that increases the pressure difference before the merging ofthe refrigerant and refrigerating machine oil returned from the lowerportion of the heat source heat exchanger 23 to the compressionmechanism 21 through the first oil returning circuit 101), and the flowrate of the refrigerating machine oil and the refrigerant returned tothe compression mechanism 21 from the lower portion of the heat sourceheat exchanger 23 through the first oil returning circuit 101 can beincreased. Thus, the refrigerating machine oil and the refrigerant of aflow rate sufficient enough to be able to prevent the refrigeratingmachine oil from accumulating inside the heat source heat exchanger 23can be returned to the compression mechanism 21 from the lower portionof the heat source heat exchanger 23 through the first oil returningcircuit 101. It will be noted that the capillary tube 131 c is not usedwhen the pressure loss in the bypass pipe 131 b can be appropriately setwithout connecting the capillary tube 131 c.

Further, rather than the control valve 131 a and the bypass pipe 131 bof the above-described pressure reducing mechanism 131, the pressurereducing mechanism acting as a pressure difference increasing mechanismmay also be an electrically powered expansion valve connected to thepipe connecting the third port 22 c of the first switch mechanism 22 andthe intake side of the compression mechanism 21, as shown in FIG. 14.This pressure reducing mechanism 141 is configured such that when thefirst oil returning circuit 101 is used, control is conducted to reducethe opening, the pressure loss from the refrigerant outlet side of theheat source heat exchanger 23 functioning as an evaporator to the intakeside of the compression mechanism 21 can be increased, and the flow rateof the refrigerating machine oil and the refrigerant returned to thecompression mechanism 21 from the lower portion of the heat source heatexchanger 23 through the first oil returning circuit 101 can beincreased, and such that in other cases, control can be conducted toincrease the opening (i.e., completely open), so that the refrigeratingmachine oil and the refrigerant of a flow rate sufficient enough to beable to prevent the refrigerating machine oil from accumulating insidethe heat source heat exchanger 23 can be reliably returned to thecompression mechanism 21 from the lower portion of the heat source heatexchanger 23 through the first oil returning circuit 101.

A pump mechanism 151 may be disposed as a pressure difference increasingmechanism, as shown in FIG. 15, in the first oil returning circuit 101rather than using the pressure reducing mechanism 131 and pressurereducing mechanism 141 as described above. For example, a refrigerantpump can be used as the pressure reducing mechanism 151. The pumpmechanism 151 can increase the flow rate of the refrigerating machineoil and the refrigerant returned to the compression mechanism 21 fromthe lower portion of the heat source heat exchanger 23 through the firstoil returning circuit 101 by increasing the pressure of therefrigerating machine oil accumulated inside the heat source heatexchanger 23 and sending the refrigerating machine oil to the first oilreturning circuit 101 (i.e., by causing the pressure reducing mechanism151 to function as a pressure difference increasing mechanism thatincreases the pressure difference before the merging of the refrigerantand refrigerating machine oil returned from the lower portion of theheat source heat exchanger 23 to the compression mechanism 21 throughthe first oil returning circuit 101). The refrigerating machine oil andthe refrigerant of a flow rate sufficient enough to be able to preventthe refrigerating machine oil from accumulating inside the heat sourceheat exchanger 23 can thereby be returned to the compression mechanism21 from the lower portion of the heat source heat exchanger 23 throughthe first oil returning circuit 101.

An ejector mechanism 161 may be disposed as the pressure differenceincreasing mechanism, as shown in FIG. 16, in place of the pump 151. Theejector mechanism 161 mainly comprises an ejector 161 a disposed in thefirst oil returning circuit 101, a branching tube 161 b in which highpressure gas refrigerant as the driving fluid of the ejector 161 abranches from the discharge side (in the present modification, betweenthe oil separator 21 b and the first port 22 a of the first switchmechanism 22) of the compression mechanism 21, and a control valve 161 cdisposed in the branching tube 161 b. In this ejector 161, in the casethat the first oil returning circuit 101 is used, the flow rate of therefrigerating machine oil and the refrigerant returned to thecompression mechanism 21 from the lower portion of the heat source heatexchanger 23 through the first oil returning circuit 101 can beincreased by opening the control valve 161 a, feeding high pressure gasrefrigerant as the driving fluid to the ejector 161 a from the dischargeside of the compression mechanism 21, using the high pressure gasrefrigerant to draw in the refrigerating machine oil accumulated in thelower portion of the heat source heat exchanger 23, and sending to intothe first oil returning circuit 101 (i.e., by causing the ejector 161 tofunction as a pressure difference increasing mechanism that increasesthe pressure difference before the merging of the refrigerant andrefrigerating machine oil returned from the lower portion of the heatsource heat exchanger 23 to the compression mechanism 21 through thefirst oil returning circuit 101). The refrigerating machine oil and therefrigerant of a flow rate sufficient enough to be able to prevent therefrigerating machine oil from accumulating inside the heat source heatexchanger 23 can thereby be reliably returned to the compressionmechanism 21 from the lower portion of the heat source heat exchanger 23through the first oil returning circuit 101.

(8) Other Embodiments

Embodiments of the present invention were described above with referenceto the diagrams, but the specific configurations are not limited tothese embodiments, and modifications are possible that do not departfrom the spirit of the present invention.

INDUSTRIAL APPLICABILITY

In accordance with the present invention, the control width can beexpanded when the evaporating ability of the evaporator is controlled bythe expansion valve in a refrigerating apparatus and air conditionerprovided with a refrigerant circuit that has an evaporator configured sothat refrigerant flows in from below and flows out from above.

1. A refrigerating apparatus, comprising: a refrigerant circuitincluding a compression mechanism, a condenser, an expansion valve, andan evaporator, the evaporator being configured so that a refrigerantflows in from below and flows out from above, and the refrigerantcircuit using a combination of a refrigerating machine oil and therefrigerant that does not separate into two layers in a temperaturerange of 30° C. or below; and an oil returning circuit connected to alower portion of the evaporator and configured to return therefrigerating machine oil accumulated inside the evaporator to thecompression mechanism together with the refrigerant.
 2. Therefrigerating apparatus of claim 1, wherein the refrigerating machineoil and the refrigerant used in the refrigerant circuit are acombination of a refrigerating machine oil and a refrigerant that doesnot separate into two layers in a temperature range of −5° C. or below.3. The refrigerating apparatus of claim 2, wherein the combination ofrefrigerating machine oil and refrigerant used in the refrigerantcircuit includes ethereal oil and R410A.
 4. The refrigerating apparatusof claim 1, further comprising a pressure difference increasingmechanism for increasing a pressure difference before merging of therefrigerating machine oil and the refrigerant returned to thecompression mechanism from the lower portion of the evaporator throughthe oil returning circuit.
 5. A refrigerating apparatus, comprising: arefrigerant circuit including a compression mechanism, a condenser, anexpansion valve, and an evaporator, the evaporator being configured sothat a refrigerant flows in from below and flows out from above, and therefrigerant circuit using a combination of a refrigerating machine oiland the refrigerant that does not separate into two layers in theevaporator; and an oil returning circuit connected to a lower portion ofthe evaporator and configured to return the refrigerating machine oilaccumulated inside the evaporator to the compression mechanism togetherwith the refrigerant.
 6. An air conditioner, comprising: a refrigerantcircuit including a plurality of utilization refrigerant circuits, eachhaving a utilization heat exchanger and a utilization expansion valveand being connected to a heat source refrigerant circuit including acompression mechanism, a heat source expansion valve and a heat sourceheat exchanger, the heat source heat exchanger being configured so thata refrigerant flows in from below and flows out from above when the heatsource heat exchanger functions as an evaporator, the heat sourcerefrigerant circuit using a combination of a refrigerating machine oiland a refrigerant that does not separate into two layers in atemperature range of 30° C. or below; and an oil returning circuitconnected to a lower portion of the heat source heat exchanger andconfigured to return the refrigerating machine oil accumulated insidethe heat source heat exchanger to the compression mechanism togetherwith the refrigerant.
 7. The air conditioner of claim 6, wherein therefrigerating machine oil and the refrigerant used in the refrigerantcircuit are a combination of a refrigerating machine oil and arefrigerant that does not separate into two layers in a temperaturerange of −5° C. or below.
 8. The air conditioner of claim 7, wherein thecombination of refrigerating machine oil and refrigerant used in therefrigerant circuit includes ethereal oil and R410A.
 9. The airconditioner of claim 6, further comprising a pressure differenceincreasing mechanism for increasing a pressure difference before mergingof the refrigerating machine oil and the refrigerant returned to thecompression mechanism from the lower portion of the heat source heatexchanger through the oil returning circuit.
 10. The air conditioner ofclaim 6, wherein the oil returning circuit has a control valve, and thecontrol valve is closed when the heat source heat exchanger functions asa condenser, and is open when the heat source heat exchanger functionsas an evaporator.
 11. The air conditioner of claim 10, wherein thecontrol valve is opened when the heat source expansion valve is at orbelow a prescribed position.
 12. The air conditioner of claim 6, whereinthe heat source heat exchanger uses as a heat source water fed at aconstant rate without regard to a flow rate of refrigerant that flowsinside the heat source heat exchanger.
 13. The air conditioner of claim6, wherein the heat source heat exchanger includes a plate heatexchanger.
 14. An air conditioner, comprising: a refrigerant circuitincluding a plurality of utilization refrigerant circuits, each having autilization heat exchanger and a utilization expansion valve and beingconnected to a heat source refrigerant circuit including a compressionmechanism, a heat source expansion valve and a heat source heatexchanger, the heat source heat exchanger being configured so that arefrigerant flows in from below and flows out from above when the heatsource heat exchanger functions as an evaporator, the heat sourcerefrigerant circuit using a combination of a refrigerating machine oiland a refrigerant that does not separate into two layers inside the heatsource heat exchanger when the heat source heat exchanger functions asan evaporator; and an oil returning circuit connected to a lower portionof the heat source heat exchanger and configured to return therefrigerating machine oil accumulated inside the heat source heatexchanger to the compression mechanism together with the refrigerant.